diff --git a/internal/runners/install/install.go b/internal/runners/install/install.go
index f0b4ce3b86..e11ca22eed 100644
--- a/internal/runners/install/install.go
+++ b/internal/runners/install/install.go
@@ -114,6 +114,7 @@ func (i *Install) Run(params Params) (rerr error) {
 	var oldCommit *bpModel.Commit
 	var reqs requirements
 	var ts time.Time
+	var override bool
 	{
 		pg = output.StartSpinner(out, locale.T("progress_search"), constants.TerminalAnimationInterval)
 
@@ -133,6 +134,7 @@ func (i *Install) Run(params Params) (rerr error) {
 		if err != nil {
 			return errs.Wrap(err, "Unable to get timestamp from params")
 		}
+		override = params.Timestamp.String() != ""
 
 		// Get languages used in current project
 		languages, err := model.FetchLanguagesForBuildScript(oldCommit.BuildScript())
@@ -153,7 +155,7 @@ func (i *Install) Run(params Params) (rerr error) {
 
 	// Prepare updated buildscript
 	script := oldCommit.BuildScript()
-	if err := prepareBuildScript(script, reqs, ts); err != nil {
+	if err := prepareBuildScript(script, reqs, ts, override); err != nil {
 		return errs.Wrap(err, "Could not prepare build script")
 	}
 
@@ -340,8 +342,8 @@ func (i *Install) renderUserFacing(reqs requirements) {
 	i.prime.Output().Notice("")
 }
 
-func prepareBuildScript(script *buildscript.BuildScript, requirements requirements, ts time.Time) error {
-	script.SetAtTime(ts)
+func prepareBuildScript(script *buildscript.BuildScript, requirements requirements, ts time.Time, override bool) error {
+	script.SetAtTime(ts, override)
 	for _, req := range requirements {
 		requirement := types.Requirement{
 			Namespace:          req.Resolved.Namespace,
diff --git a/internal/runners/platforms/add.go b/internal/runners/platforms/add.go
index b4d8d5c253..5b4d7b4300 100644
--- a/internal/runners/platforms/add.go
+++ b/internal/runners/platforms/add.go
@@ -98,7 +98,7 @@ func (a *Add) Run(params AddRunParams) (rerr error) {
 
 	// Prepare updated buildscript
 	script := oldCommit.BuildScript()
-	script.SetAtTime(ts)
+	script.SetAtTime(ts, false)
 	script.AddPlatform(*platform.PlatformID)
 
 	// Update local checkout and source runtime changes
diff --git a/internal/runners/upgrade/upgrade.go b/internal/runners/upgrade/upgrade.go
index 953b20098c..ec1320542d 100644
--- a/internal/runners/upgrade/upgrade.go
+++ b/internal/runners/upgrade/upgrade.go
@@ -111,7 +111,7 @@ func (u *Upgrade) Run(params *Params) (rerr error) {
 	if err != nil {
 		return errs.Wrap(err, "Failed to fetch latest timestamp")
 	}
-	bumpedBS.SetAtTime(ts)
+	bumpedBS.SetAtTime(ts, params.Timestamp.String() != "")
 
 	// Since our platform is commit based we need to create a commit for the "after" buildplan, even though we may not
 	// end up using it it the user doesn't confirm the upgrade.
diff --git a/pkg/buildscript/buildscript.go b/pkg/buildscript/buildscript.go
index 30e9b3b264..79ad6b7474 100644
--- a/pkg/buildscript/buildscript.go
+++ b/pkg/buildscript/buildscript.go
@@ -19,11 +19,6 @@ type BuildScript struct {
 
 	project string
 	atTime  *time.Time
-
-	// solveAtTime is the original at_time found in the solve node.
-	// This is used to support the legacy use case where the at_time
-	// is an actual time stamp and not a reference to the $at_time variable.
-	solveAtTime *time.Time
 }
 
 func init() {
@@ -58,15 +53,13 @@ func (b *BuildScript) SetProject(url string) {
 }
 
 func (b *BuildScript) AtTime() *time.Time {
-	// If the atTime is set, prefer that over the
-	// legacy solveAtTime.
-	if b.atTime != nil {
-		return b.atTime
-	}
-	return b.solveAtTime
+	return b.atTime
 }
 
-func (b *BuildScript) SetAtTime(t time.Time) {
+func (b *BuildScript) SetAtTime(t time.Time, override bool) {
+	if b.atTime != nil && !override {
+		return
+	}
 	b.atTime = &t
 }
 
diff --git a/pkg/buildscript/buildscript_test.go b/pkg/buildscript/buildscript_test.go
index 7d2ccbe0fe..4bc18a2d06 100644
--- a/pkg/buildscript/buildscript_test.go
+++ b/pkg/buildscript/buildscript_test.go
@@ -127,18 +127,30 @@ func TestRoundTripFromBuildExpressionWithLegacyAtTime(t *testing.T) {
 	assert.Contains(t, string(data), "$at_time")
 	assert.NotContains(t, string(data), initialTimeStamp)
 
-	// Update the time in the build script
+	// Update the time in the build script but don't override the existing time
 	updatedTime, err := time.Parse(strfmt.RFC3339Millis, updatedTimeStamp)
 	require.NoError(t, err)
-	script.SetAtTime(updatedTime)
+	script.SetAtTime(updatedTime, false)
 
 	// The updated time should be reflected in the build script
-	require.Equal(t, updatedTime, *script.AtTime())
+	require.Equal(t, initialTimeStamp, script.AtTime().Format(strfmt.RFC3339Millis))
 
 	data, err = script.Marshal()
 	require.NoError(t, err)
 
-	// The marshalled build script should now contain the updated time
+	// The marshalled build script should NOT contain the updated time
+	// in the Time block at the top of the script.
+	assert.Contains(t, string(data), initialTimeStamp)
+	assert.NotContains(t, string(data), fmt.Sprintf("Time: %s", updatedTime))
+
+	// Now override the time in the build script
+	script.SetAtTime(updatedTime, true)
+	require.Equal(t, updatedTimeStamp, script.AtTime().Format(strfmt.RFC3339Millis))
+
+	data, err = script.Marshal()
+	require.NoError(t, err)
+
+	// The marshalled build script should NOW contain the updated time
 	// in the Time block at the top of the script.
 	assert.Contains(t, string(data), updatedTimeStamp)
 	assert.NotContains(t, string(data), fmt.Sprintf("Time: %s", initialTimeStamp))
@@ -158,7 +170,7 @@ func TestExpressionToScript(t *testing.T) {
 
 	script := New()
 	script.SetProject(testProject)
-	script.SetAtTime(ts)
+	script.SetAtTime(ts, false)
 	require.NoError(t, script.UnmarshalBuildExpression(basicBuildExpression))
 
 	data, err := script.Marshal()
diff --git a/pkg/buildscript/merge.go b/pkg/buildscript/merge.go
index 889cafffb1..32db4da729 100644
--- a/pkg/buildscript/merge.go
+++ b/pkg/buildscript/merge.go
@@ -58,7 +58,7 @@ func (b *BuildScript) Merge(other *BuildScript, strategies *mono_models.MergeStr
 	// When merging build scripts we want to use the most recent timestamp
 	atTime := other.AtTime()
 	if atTime != nil && b.AtTime() != nil && atTime.After(*b.AtTime()) {
-		b.SetAtTime(*atTime)
+		b.SetAtTime(*atTime, true)
 	}
 
 	return nil
diff --git a/pkg/buildscript/unmarshal.go b/pkg/buildscript/unmarshal.go
index 4719b63460..9602aef76c 100644
--- a/pkg/buildscript/unmarshal.go
+++ b/pkg/buildscript/unmarshal.go
@@ -79,5 +79,5 @@ func Unmarshal(data []byte) (*BuildScript, error) {
 		atTime = ptr.To(time.Time(atTimeStr))
 	}
 
-	return &BuildScript{raw, project, atTime, nil}, nil
+	return &BuildScript{raw, project, atTime}, nil
 }
diff --git a/pkg/buildscript/unmarshal_buildexpression.go b/pkg/buildscript/unmarshal_buildexpression.go
index 959d6303b8..fe7eee2eeb 100644
--- a/pkg/buildscript/unmarshal_buildexpression.go
+++ b/pkg/buildscript/unmarshal_buildexpression.go
@@ -77,7 +77,7 @@ func (b *BuildScript) UnmarshalBuildExpression(data []byte) error {
 			atTimeNode.Str = nil
 			atTimeNode.Ident = ptr.To("TIME")
 			// Preserve the original at_time found in the solve node.
-			b.solveAtTime = ptr.To(time.Time(atTime))
+			b.atTime = ptr.To(time.Time(atTime))
 		} else if atTimeNode.Ident != nil && *atTimeNode.Ident == "at_time" {
 			atTimeNode.Ident = ptr.To("TIME")
 		}
diff --git a/pkg/platform/model/buildplanner/build.go b/pkg/platform/model/buildplanner/build.go
index 0b11fc1712..feef9b1a28 100644
--- a/pkg/platform/model/buildplanner/build.go
+++ b/pkg/platform/model/buildplanner/build.go
@@ -110,7 +110,7 @@ func (b *BuildPlanner) FetchCommit(commitID strfmt.UUID, owner, project string,
 	if err := script.UnmarshalBuildExpression(commit.Expression); err != nil {
 		return nil, errs.Wrap(err, "failed to parse build expression")
 	}
-	script.SetAtTime(time.Time(commit.AtTime))
+	script.SetAtTime(time.Time(commit.AtTime), false)
 
 	return &Commit{commit, bp, script}, nil
 }
diff --git a/pkg/platform/model/buildplanner/buildscript.go b/pkg/platform/model/buildplanner/buildscript.go
index 28bd980ffc..c6fcc6a2ee 100644
--- a/pkg/platform/model/buildplanner/buildscript.go
+++ b/pkg/platform/model/buildplanner/buildscript.go
@@ -52,7 +52,7 @@ func (b *BuildPlanner) GetBuildScript(commitID string) (*buildscript.BuildScript
 	}
 
 	script := buildscript.New()
-	script.SetAtTime(time.Time(resp.Commit.AtTime))
+	script.SetAtTime(time.Time(resp.Commit.AtTime), false)
 	if err := script.UnmarshalBuildExpression(resp.Commit.Expression); err != nil {
 		return nil, errs.Wrap(err, "failed to parse build expression")
 	}
diff --git a/pkg/platform/model/buildplanner/commit.go b/pkg/platform/model/buildplanner/commit.go
index 387296b1ff..3086d32930 100644
--- a/pkg/platform/model/buildplanner/commit.go
+++ b/pkg/platform/model/buildplanner/commit.go
@@ -82,7 +82,7 @@ func (b *BuildPlanner) StageCommit(params StageCommitParams) (*Commit, error) {
 	}
 
 	stagedScript := buildscript.New()
-	stagedScript.SetAtTime(time.Time(resp.Commit.AtTime))
+	stagedScript.SetAtTime(time.Time(resp.Commit.AtTime), false)
 	if err := stagedScript.UnmarshalBuildExpression(resp.Commit.Expression); err != nil {
 		return nil, errs.Wrap(err, "failed to parse build expression")
 	}
diff --git a/scripts/to-buildscript/main.go b/scripts/to-buildscript/main.go
index 60c7cde520..84a2e4599f 100644
--- a/scripts/to-buildscript/main.go
+++ b/scripts/to-buildscript/main.go
@@ -55,7 +55,7 @@ func main() {
 	bs := buildscript.New()
 	bs.SetProject(project)
 	if atTime != nil {
-		bs.SetAtTime(*atTime)
+		bs.SetAtTime(*atTime, true)
 	}
 	err := bs.UnmarshalBuildExpression([]byte(input))
 	if err != nil {