diff --git a/assets/js/components/Optimize/TimeSeriesDataTable.vue b/assets/js/components/Optimize/TimeSeriesDataTable.vue
index 796c96a97..2bf0d63d6 100644
--- a/assets/js/components/Optimize/TimeSeriesDataTable.vue
+++ b/assets/js/components/Optimize/TimeSeriesDataTable.vue
@@ -218,9 +218,9 @@ export default defineComponent({
 			type: Array as PropType<BatteryDetail[]>,
 			required: true,
 		},
-		timestamp: {
-			type: String,
-			default: "",
+		timestamps: {
+			type: Array as PropType<string[]>,
+			default: () => [],
 		},
 		currency: {
 			type: String as PropType<CURRENCY>,
@@ -262,13 +262,16 @@ export default defineComponent({
 			return (seconds / 3600).toFixed(2);
 		},
 		formatHour(index: number): string {
-			// Show label only every 4th slot (every hour for 15-minute slots)
-			if (index % 4 !== 0) {
+			if (this.timestamps.length <= index) {
 				return "";
 			}
-			const startTime = new Date(this.timestamp);
-			const currentTime = new Date(startTime.getTime() + index * 15 * 60 * 1000); // Add 15-minute intervals
-			return currentTime.getHours().toString();
+			// Show label on fresh hour or on first quarter hour for slot 0
+			const ts = new Date(this.timestamps[index]);
+			const minutes = ts.getMinutes();
+			if (minutes === 0 || (index === 0 && minutes < 15)) {
+				return ts.getHours().toString();
+			}
+			return "";
 		},
 		getBatteryTitle(index: number): string {
 			const detail = this.batteryDetails[index];
diff --git a/assets/js/views/Optimize.vue b/assets/js/views/Optimize.vue
index 3a133b713..77126ec81 100644
--- a/assets/js/views/Optimize.vue
+++ b/assets/js/views/Optimize.vue
@@ -82,7 +82,7 @@
 						<TimeSeriesDataTable
 							:evopt="evopt"
 							:battery-details="evopt.details.batteryDetails"
-							:timestamp="evopt.details.timestamp[0]"
+							:timestamps="evopt.details.timestamp"
 							:currency="currency"
 							:battery-colors="batteryColors"
 							:dimmed-battery-colors="dimmedBatteryColors"
diff --git a/core/site_optimizer.go b/core/site_optimizer.go
index b79659067..b351a9596 100644
--- a/core/site_optimizer.go
+++ b/core/site_optimizer.go
@@ -144,7 +144,8 @@ func (site *Site) optimizerUpdate(battery []types.Measurement) error {
 		return fmt.Errorf("not enough slots for optimization: %d (grid=%d, feedIn=%d, solar=%d)", minLen, len(grid), len(feedIn), len(solar))
 	}
 
-	dt := timeSteps(minLen)
+	now := time.Now()
+	dt := timeSteps(minLen, now)
 	firstSlotDuration := time.Duration(dt[0]) * time.Second
 
 	site.log.DEBUG.Printf("optimizer: optimizing %d slots until %v: grid=%d, feedIn=%d, solar=%d, first slot: %v",
@@ -190,7 +191,7 @@ func (site *Site) optimizerUpdate(battery []types.Measurement) error {
 	pa := lo.Min(req.TimeSeries.PN) * eta * 0.99
 
 	details := requestDetails{
-		Timestamps: asTimestamps(dt),
+		Timestamps: asTimestamps(dt, now),
 	}
 
 	if site.circuit != nil {
@@ -588,10 +589,6 @@ func solarRatesToEnergy(rr api.Rates) (api.Rates, error) {
 	return res, nil
 }
 
-func endOfHour(ts time.Time) time.Time {
-	return ts.Truncate(time.Hour).Add(time.Hour)
-}
-
 func currentRates(tariff api.Tariff) api.Rates {
 	if tariff == nil {
 		return nil
@@ -609,12 +606,11 @@ func currentRates(tariff api.Tariff) api.Rates {
 	})
 }
 
-func timeSteps(minLen int) []int {
+func timeSteps(minLen int, now time.Time) []int {
 	res := make([]int, 0, minLen)
 
-	bos := time.Now().Truncate(tariff.SlotDuration)
-	eos := bos.Add(tariff.SlotDuration)
-	if d := time.Until(eos); d > time.Second && d < tariff.SlotDuration {
+	eos := now.Truncate(tariff.SlotDuration).Add(tariff.SlotDuration)
+	if d := eos.Sub(now); d > time.Second && d < tariff.SlotDuration {
 		res = append(res, int(d.Seconds()))
 	}
 
@@ -625,13 +621,16 @@ func timeSteps(minLen int) []int {
 	return res
 }
 
-func asTimestamps(dt []int) []time.Time {
+func asTimestamps(dt []int, now time.Time) []time.Time {
 	res := make([]time.Time, 0, len(dt))
-	eoh := endOfHour(time.Now())
-	res = append(res, eoh.Add(-time.Duration(dt[0])*time.Second))
+
+	eos := now.Truncate(tariff.SlotDuration).Add(tariff.SlotDuration)
+	res = append(res, eos.Add(-time.Duration(dt[0])*time.Second))
+
 	for i := range len(dt) - 1 {
-		res = append(res, eoh.Add(time.Duration(dt[i+1])*time.Second))
+		res = append(res, res[i].Add(time.Duration(dt[i])*time.Second))
 	}
+
 	return res
 }
 
diff --git a/core/site_optimizer_test.go b/core/site_optimizer_test.go
index 70fda2362..ca8e86146 100644
--- a/core/site_optimizer_test.go
+++ b/core/site_optimizer_test.go
@@ -111,6 +111,26 @@ func TestLoadpointProfile(t *testing.T) {
 	require.Equal(t, []float64{250, 250, 250, 250, 250, 250, 250, 50}, loadpointProfile(lp, 8))
 }
 
+func TestAsTimestamps(t *testing.T) {
+	// now is 10 minutes into a 15-minute slot
+	now := time.Date(2025, 1, 1, 12, 10, 0, 0, time.UTC)
+
+	// dt[0]=300 means first event is 300s (5min) before end of current slot
+	// dt[1..] just mark subsequent slot boundaries
+	dt := []int{60 * 5, 60 * 15, 60 * 15}
+
+	got := asTimestamps(dt, now)
+
+	// current slot: 12:00–12:15
+	// first timestamp: 12:15 - 5min = 12:10
+	// subsequent: 12:15, 12:30
+	assert.Equal(t, []time.Time{
+		time.Date(2025, 1, 1, 12, 10, 0, 0, time.UTC),
+		time.Date(2025, 1, 1, 12, 15, 0, 0, time.UTC),
+		time.Date(2025, 1, 1, 12, 30, 0, 0, time.UTC),
+	}, got)
+}
+
 func TestBatteryForecastTotals(t *testing.T) {
 	site := new(Site)