diff --git a/pkg/models/geo.go b/pkg/models/geo.go
index b8c8ffe19..5f27db85a 100644
--- a/pkg/models/geo.go
+++ b/pkg/models/geo.go
@@ -112,9 +112,13 @@ func (pcg precomputedCellGeometry) CalculateCovering() (s2.CellUnion, error) {
 // * geo.ErrRadiusMustBeLargerThan0
 func UnionVolumes4D(volumes ...*Volume4D) (*Volume4D, error) {
 	result := &Volume4D{}
+	var unboundedStartTime, unboundedEndTime bool
 
 	for _, volume := range volumes {
-		if volume.EndTime != nil {
+		if volume.EndTime == nil {
+			unboundedEndTime = true
+			result.EndTime = nil
+		} else if !unboundedEndTime {
 			if result.EndTime != nil {
 				if volume.EndTime.After(*result.EndTime) {
 					*result.EndTime = *volume.EndTime
@@ -124,7 +128,10 @@ func UnionVolumes4D(volumes ...*Volume4D) (*Volume4D, error) {
 			}
 		}
 
-		if volume.StartTime != nil {
+		if volume.StartTime == nil {
+			unboundedStartTime = true
+			result.StartTime = nil
+		} else if !unboundedStartTime {
 			if result.StartTime != nil {
 				if volume.StartTime.Before(*result.StartTime) {
 					*result.StartTime = *volume.StartTime
diff --git a/pkg/models/geo_test.go b/pkg/models/geo_test.go
index 148d25108..747448a7a 100644
--- a/pkg/models/geo_test.go
+++ b/pkg/models/geo_test.go
@@ -2,8 +2,10 @@ package models
 
 import (
 	"testing"
+	"time"
 
 	"github.com/golang/geo/s2"
+	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
 )
 
@@ -53,3 +55,71 @@ func TestPolygonCovering(t *testing.T) {
 	require.NoError(t, err)
 	require.Equal(t, want, got)
 }
+
+func TestUnionVolumes4D_Time(t *testing.T) {
+	now := time.Now()
+	start := now.Add(time.Hour)
+	end := start.Add(time.Hour)
+
+	nextStart := end.Add(time.Hour)
+	nextEnd := nextStart.Add(time.Hour)
+
+	tests := []struct {
+		name          string
+		volumes       []*Volume4D
+		wantStartTime *time.Time
+		wantEndTime   *time.Time
+	}{
+		{
+			name:          "unbounded",
+			volumes:       []*Volume4D{{}},
+			wantStartTime: nil,
+			wantEndTime:   nil,
+		},
+		{
+			name:          "single bounded",
+			volumes:       []*Volume4D{{StartTime: &start, EndTime: &end}},
+			wantStartTime: &start,
+			wantEndTime:   &end,
+		},
+		{
+			name:          "single unbounded start",
+			volumes:       []*Volume4D{{EndTime: &end}},
+			wantStartTime: nil,
+			wantEndTime:   &end,
+		},
+		{
+			name:          "single unbounded end",
+			volumes:       []*Volume4D{{StartTime: &start}},
+			wantStartTime: &start,
+			wantEndTime:   nil,
+		},
+		{
+			name:          "multiple bounded",
+			volumes:       []*Volume4D{{StartTime: &start, EndTime: &end}, {StartTime: &nextStart, EndTime: &nextEnd}},
+			wantStartTime: &start,
+			wantEndTime:   &nextEnd,
+		},
+		{
+			name:          "multiple unbounded",
+			volumes:       []*Volume4D{{StartTime: &start, EndTime: &end}, {}},
+			wantStartTime: nil,
+			wantEndTime:   nil,
+		},
+		{
+			name:          "multiple unbounded combination",
+			volumes:       []*Volume4D{{StartTime: &start}, {EndTime: &nextEnd}},
+			wantStartTime: nil,
+			wantEndTime:   nil,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			union, err := UnionVolumes4D(tt.volumes...)
+			require.NoError(t, err)
+			assert.Equal(t, tt.wantStartTime, union.StartTime)
+			assert.Equal(t, tt.wantEndTime, union.EndTime)
+		})
+	}
+}