diff --git a/PENDING.md b/PENDING.md
index 46e861013..51d80bd5b 100644
--- a/PENDING.md
+++ b/PENDING.md
@@ -23,6 +23,7 @@ BREAKING CHANGES
     * [core] \#1807 Switch from use of rational to decimal
     * [types] \#1901 Validator interface's GetOwner() renamed to GetOperator()
     * [types] \#2119 Parsed error messages and ABCI log errors to make them more human readable.
+    * [simulation] Rename TestAndRunTx to Operation [#2153](https://github.com/cosmos/cosmos-sdk/pull/2153)
 
 * Tendermint
 
@@ -60,6 +61,7 @@ IMPROVEMENTS
 * SDK
     * [tools] Make get_vendor_deps deletes `.vendor-new` directories, in case scratch files are present.
     * [cli] \#1632 Add integration tests to ensure `basecoind init && basecoind` start sequences run successfully for both `democoin` and `basecoin` examples.
+    * [simulation] Make timestamps randomized [#2153](https://github.com/cosmos/cosmos-sdk/pull/2153)
 
 * Tendermint
 
diff --git a/cmd/gaia/app/sim_test.go b/cmd/gaia/app/sim_test.go
index 5fa75a931..9036c7e14 100644
--- a/cmd/gaia/app/sim_test.go
+++ b/cmd/gaia/app/sim_test.go
@@ -85,8 +85,8 @@ func appStateFn(r *rand.Rand, keys []crypto.PrivKey, accs []sdk.AccAddress) json
 	return appState
 }
 
-func testAndRunTxs(app *GaiaApp) []simulation.TestAndRunTx {
-	return []simulation.TestAndRunTx{
+func testAndRunTxs(app *GaiaApp) []simulation.Operation {
+	return []simulation.Operation{
 		banksim.TestAndRunSingleInputMsgSend(app.accountMapper),
 		govsim.SimulateMsgSubmitProposal(app.govKeeper, app.stakeKeeper),
 		govsim.SimulateMsgDeposit(app.govKeeper, app.stakeKeeper),
diff --git a/x/bank/simulation/msgs.go b/x/bank/simulation/msgs.go
index 43d7e1fd7..633f6787f 100644
--- a/x/bank/simulation/msgs.go
+++ b/x/bank/simulation/msgs.go
@@ -20,7 +20,7 @@ import (
 
 // TestAndRunSingleInputMsgSend tests and runs a single msg send, with one input and one output, where both
 // accounts already exist.
-func TestAndRunSingleInputMsgSend(mapper auth.AccountMapper) simulation.TestAndRunTx {
+func TestAndRunSingleInputMsgSend(mapper auth.AccountMapper) simulation.Operation {
 	return func(t *testing.T, r *rand.Rand, app *baseapp.BaseApp, ctx sdk.Context, keys []crypto.PrivKey, log string, event func(string)) (action string, err sdk.Error) {
 		fromKey := simulation.RandomKey(r, keys)
 		fromAddr := sdk.AccAddress(fromKey.PubKey().Address())
diff --git a/x/bank/simulation/sim_test.go b/x/bank/simulation/sim_test.go
index 8fedeca79..88e7a5f3a 100644
--- a/x/bank/simulation/sim_test.go
+++ b/x/bank/simulation/sim_test.go
@@ -33,7 +33,7 @@ func TestBankWithRandomMessages(t *testing.T) {
 
 	simulation.Simulate(
 		t, mapp.BaseApp, appStateFn,
-		[]simulation.TestAndRunTx{
+		[]simulation.Operation{
 			TestAndRunSingleInputMsgSend(mapper),
 		},
 		[]simulation.RandSetup{},
diff --git a/x/gov/simulation/msgs.go b/x/gov/simulation/msgs.go
index ed80ab4e6..f270d3a7d 100644
--- a/x/gov/simulation/msgs.go
+++ b/x/gov/simulation/msgs.go
@@ -21,7 +21,7 @@ const (
 )
 
 // SimulateMsgSubmitProposal
-func SimulateMsgSubmitProposal(k gov.Keeper, sk stake.Keeper) simulation.TestAndRunTx {
+func SimulateMsgSubmitProposal(k gov.Keeper, sk stake.Keeper) simulation.Operation {
 	return func(t *testing.T, r *rand.Rand, app *baseapp.BaseApp, ctx sdk.Context, keys []crypto.PrivKey, log string, event func(string)) (action string, err sdk.Error) {
 		key := simulation.RandomKey(r, keys)
 		addr := sdk.AccAddress(key.PubKey().Address())
@@ -50,7 +50,7 @@ func SimulateMsgSubmitProposal(k gov.Keeper, sk stake.Keeper) simulation.TestAnd
 }
 
 // SimulateMsgDeposit
-func SimulateMsgDeposit(k gov.Keeper, sk stake.Keeper) simulation.TestAndRunTx {
+func SimulateMsgDeposit(k gov.Keeper, sk stake.Keeper) simulation.Operation {
 	return func(t *testing.T, r *rand.Rand, app *baseapp.BaseApp, ctx sdk.Context, keys []crypto.PrivKey, log string, event func(string)) (action string, err sdk.Error) {
 		key := simulation.RandomKey(r, keys)
 		addr := sdk.AccAddress(key.PubKey().Address())
@@ -77,7 +77,7 @@ func SimulateMsgDeposit(k gov.Keeper, sk stake.Keeper) simulation.TestAndRunTx {
 }
 
 // SimulateMsgVote
-func SimulateMsgVote(k gov.Keeper, sk stake.Keeper) simulation.TestAndRunTx {
+func SimulateMsgVote(k gov.Keeper, sk stake.Keeper) simulation.Operation {
 	return func(t *testing.T, r *rand.Rand, app *baseapp.BaseApp, ctx sdk.Context, keys []crypto.PrivKey, log string, event func(string)) (action string, err sdk.Error) {
 		key := simulation.RandomKey(r, keys)
 		addr := sdk.AccAddress(key.PubKey().Address())
diff --git a/x/gov/simulation/sim_test.go b/x/gov/simulation/sim_test.go
index 691aa1cd2..6f0f9830c 100644
--- a/x/gov/simulation/sim_test.go
+++ b/x/gov/simulation/sim_test.go
@@ -55,7 +55,7 @@ func TestGovWithRandomMessages(t *testing.T) {
 
 	simulation.Simulate(
 		t, mapp.BaseApp, appStateFn,
-		[]simulation.TestAndRunTx{
+		[]simulation.Operation{
 			SimulateMsgSubmitProposal(govKeeper, stakeKeeper),
 			SimulateMsgDeposit(govKeeper, stakeKeeper),
 			SimulateMsgVote(govKeeper, stakeKeeper),
diff --git a/x/mock/simulation/random_simulate_blocks.go b/x/mock/simulation/random_simulate_blocks.go
index c7e616614..5b1d4030c 100644
--- a/x/mock/simulation/random_simulate_blocks.go
+++ b/x/mock/simulation/random_simulate_blocks.go
@@ -3,6 +3,7 @@ package simulation
 import (
 	"encoding/json"
 	"fmt"
+	"math"
 	"math/rand"
 	"sort"
 	"testing"
@@ -20,7 +21,7 @@ import (
 
 // Simulate tests application by sending random messages.
 func Simulate(
-	t *testing.T, app *baseapp.BaseApp, appStateFn func(r *rand.Rand, keys []crypto.PrivKey, accs []sdk.AccAddress) json.RawMessage, ops []TestAndRunTx, setups []RandSetup,
+	t *testing.T, app *baseapp.BaseApp, appStateFn func(r *rand.Rand, keys []crypto.PrivKey, accs []sdk.AccAddress) json.RawMessage, ops []Operation, setups []RandSetup,
 	invariants []Invariant, numBlocks int, blockSize int, commit bool,
 ) {
 	time := time.Now().UnixNano()
@@ -30,12 +31,20 @@ func Simulate(
 // SimulateFromSeed tests an application by running the provided
 // operations, testing the provided invariants, but using the provided seed.
 func SimulateFromSeed(
-	t *testing.T, app *baseapp.BaseApp, appStateFn func(r *rand.Rand, keys []crypto.PrivKey, accs []sdk.AccAddress) json.RawMessage, seed int64, ops []TestAndRunTx, setups []RandSetup,
+	t *testing.T, app *baseapp.BaseApp, appStateFn func(r *rand.Rand, keys []crypto.PrivKey, accs []sdk.AccAddress) json.RawMessage, seed int64, ops []Operation, setups []RandSetup,
 	invariants []Invariant, numBlocks int, blockSize int, commit bool,
 ) {
 	log := fmt.Sprintf("Starting SimulateFromSeed with randomness created with seed %d", int(seed))
-	fmt.Printf("%s\n", log)
 	r := rand.New(rand.NewSource(seed))
+
+	unixTime := r.Int63n(int64(math.Pow(2, 40)))
+
+	// Set the timestamp for simulation
+	timestamp := time.Unix(unixTime, 0)
+	log = fmt.Sprintf("%s\nStarting the simulation from time %v, unixtime %v", log, timestamp.UTC().Format(time.UnixDate), timestamp.Unix())
+	fmt.Printf("%s\n", log)
+	timeDiff := maxTimePerBlock - minTimePerBlock
+
 	keys, accs := mock.GeneratePrivKeyAddressPairsFromRand(r, numKeys)
 
 	// Setup event stats
@@ -45,9 +54,6 @@ func SimulateFromSeed(
 		events[what]++
 	}
 
-	timestamp := time.Unix(0, 0)
-	timeDiff := maxTimePerBlock - minTimePerBlock
-
 	res := app.InitChain(abci.RequestInitChain{AppStateBytes: appStateFn(r, keys, accs)})
 	validators := make(map[string]mockValidator)
 	for _, validator := range res.Validators {
diff --git a/x/mock/simulation/types.go b/x/mock/simulation/types.go
index 35769b0b2..3ece3c2e9 100644
--- a/x/mock/simulation/types.go
+++ b/x/mock/simulation/types.go
@@ -11,10 +11,15 @@ import (
 )
 
 type (
-	// TestAndRunTx produces a fuzzed transaction, and ensures the state
-	// transition was as expected. It returns a descriptive message "action"
-	// about what this fuzzed tx actually did, for ease of debugging.
-	TestAndRunTx func(
+	// Operation runs a state machine transition,
+	// and ensures the transition happened as expected.
+	// The operation could be running and testing a fuzzed transaction,
+	// or doing the same for a message.
+	//
+	// For ease of debugging,
+	// an operation returns a descriptive message "action",
+	// which details what this fuzzed state machine transition actually did.
+	Operation func(
 		t *testing.T, r *rand.Rand, app *baseapp.BaseApp, ctx sdk.Context,
 		privKeys []crypto.PrivKey, log string, event func(string),
 	) (action string, err sdk.Error)
diff --git a/x/slashing/simulation/msgs.go b/x/slashing/simulation/msgs.go
index 8ef24493b..e694bd1d7 100644
--- a/x/slashing/simulation/msgs.go
+++ b/x/slashing/simulation/msgs.go
@@ -16,7 +16,7 @@ import (
 )
 
 // SimulateMsgUnjail
-func SimulateMsgUnjail(k slashing.Keeper) simulation.TestAndRunTx {
+func SimulateMsgUnjail(k slashing.Keeper) simulation.Operation {
 	return func(t *testing.T, r *rand.Rand, app *baseapp.BaseApp, ctx sdk.Context, keys []crypto.PrivKey, log string, event func(string)) (action string, err sdk.Error) {
 		key := simulation.RandomKey(r, keys)
 		address := sdk.AccAddress(key.PubKey().Address())
diff --git a/x/stake/simulation/msgs.go b/x/stake/simulation/msgs.go
index 17f980893..995e4f358 100644
--- a/x/stake/simulation/msgs.go
+++ b/x/stake/simulation/msgs.go
@@ -18,7 +18,7 @@ import (
 )
 
 // SimulateMsgCreateValidator
-func SimulateMsgCreateValidator(m auth.AccountMapper, k stake.Keeper) simulation.TestAndRunTx {
+func SimulateMsgCreateValidator(m auth.AccountMapper, k stake.Keeper) simulation.Operation {
 	return func(t *testing.T, r *rand.Rand, app *baseapp.BaseApp, ctx sdk.Context, keys []crypto.PrivKey, log string, event func(string)) (action string, err sdk.Error) {
 		denom := k.GetParams(ctx).BondDenom
 		description := stake.Description{
@@ -55,7 +55,7 @@ func SimulateMsgCreateValidator(m auth.AccountMapper, k stake.Keeper) simulation
 }
 
 // SimulateMsgEditValidator
-func SimulateMsgEditValidator(k stake.Keeper) simulation.TestAndRunTx {
+func SimulateMsgEditValidator(k stake.Keeper) simulation.Operation {
 	return func(t *testing.T, r *rand.Rand, app *baseapp.BaseApp, ctx sdk.Context, keys []crypto.PrivKey, log string, event func(string)) (action string, err sdk.Error) {
 		description := stake.Description{
 			Moniker:  simulation.RandStringOfLength(r, 10),
@@ -83,7 +83,7 @@ func SimulateMsgEditValidator(k stake.Keeper) simulation.TestAndRunTx {
 }
 
 // SimulateMsgDelegate
-func SimulateMsgDelegate(m auth.AccountMapper, k stake.Keeper) simulation.TestAndRunTx {
+func SimulateMsgDelegate(m auth.AccountMapper, k stake.Keeper) simulation.Operation {
 	return func(t *testing.T, r *rand.Rand, app *baseapp.BaseApp, ctx sdk.Context, keys []crypto.PrivKey, log string, event func(string)) (action string, err sdk.Error) {
 		denom := k.GetParams(ctx).BondDenom
 		validatorKey := simulation.RandomKey(r, keys)
@@ -115,7 +115,7 @@ func SimulateMsgDelegate(m auth.AccountMapper, k stake.Keeper) simulation.TestAn
 }
 
 // SimulateMsgBeginUnbonding
-func SimulateMsgBeginUnbonding(m auth.AccountMapper, k stake.Keeper) simulation.TestAndRunTx {
+func SimulateMsgBeginUnbonding(m auth.AccountMapper, k stake.Keeper) simulation.Operation {
 	return func(t *testing.T, r *rand.Rand, app *baseapp.BaseApp, ctx sdk.Context, keys []crypto.PrivKey, log string, event func(string)) (action string, err sdk.Error) {
 		denom := k.GetParams(ctx).BondDenom
 		validatorKey := simulation.RandomKey(r, keys)
@@ -147,7 +147,7 @@ func SimulateMsgBeginUnbonding(m auth.AccountMapper, k stake.Keeper) simulation.
 }
 
 // SimulateMsgCompleteUnbonding
-func SimulateMsgCompleteUnbonding(k stake.Keeper) simulation.TestAndRunTx {
+func SimulateMsgCompleteUnbonding(k stake.Keeper) simulation.Operation {
 	return func(t *testing.T, r *rand.Rand, app *baseapp.BaseApp, ctx sdk.Context, keys []crypto.PrivKey, log string, event func(string)) (action string, err sdk.Error) {
 		validatorKey := simulation.RandomKey(r, keys)
 		validatorAddress := sdk.AccAddress(validatorKey.PubKey().Address())
@@ -170,7 +170,7 @@ func SimulateMsgCompleteUnbonding(k stake.Keeper) simulation.TestAndRunTx {
 }
 
 // SimulateMsgBeginRedelegate
-func SimulateMsgBeginRedelegate(m auth.AccountMapper, k stake.Keeper) simulation.TestAndRunTx {
+func SimulateMsgBeginRedelegate(m auth.AccountMapper, k stake.Keeper) simulation.Operation {
 	return func(t *testing.T, r *rand.Rand, app *baseapp.BaseApp, ctx sdk.Context, keys []crypto.PrivKey, log string, event func(string)) (action string, err sdk.Error) {
 		denom := k.GetParams(ctx).BondDenom
 		sourceValidatorKey := simulation.RandomKey(r, keys)
@@ -206,7 +206,7 @@ func SimulateMsgBeginRedelegate(m auth.AccountMapper, k stake.Keeper) simulation
 }
 
 // SimulateMsgCompleteRedelegate
-func SimulateMsgCompleteRedelegate(k stake.Keeper) simulation.TestAndRunTx {
+func SimulateMsgCompleteRedelegate(k stake.Keeper) simulation.Operation {
 	return func(t *testing.T, r *rand.Rand, app *baseapp.BaseApp, ctx sdk.Context, keys []crypto.PrivKey, log string, event func(string)) (action string, err sdk.Error) {
 		validatorSrcKey := simulation.RandomKey(r, keys)
 		validatorSrcAddress := sdk.AccAddress(validatorSrcKey.PubKey().Address())
diff --git a/x/stake/simulation/sim_test.go b/x/stake/simulation/sim_test.go
index 84745cd1d..c5d301c56 100644
--- a/x/stake/simulation/sim_test.go
+++ b/x/stake/simulation/sim_test.go
@@ -44,7 +44,7 @@ func TestStakeWithRandomMessages(t *testing.T) {
 
 	simulation.Simulate(
 		t, mapp.BaseApp, appStateFn,
-		[]simulation.TestAndRunTx{
+		[]simulation.Operation{
 			SimulateMsgCreateValidator(mapper, stakeKeeper),
 			SimulateMsgEditValidator(stakeKeeper),
 			SimulateMsgDelegate(mapper, stakeKeeper),