diff --git a/components/Timetable.vue b/components/Timetable.vue
index 5a7526b..bb30b90 100644
--- a/components/Timetable.vue
+++ b/components/Timetable.vue
@@ -75,7 +75,7 @@ const oneMinMs = 60 * 1000;
 type Edge = { type: "start" | "end", slot: TimeSlot };
 
 /** Point in time where multiple edges meet. */
-type Junction = { ts: string, edges: Edge[] };
+type Junction = { ts: number, edges: Edge[] };
 
 /** Span of time between two adjacent junctions */
 type Span = {
@@ -90,8 +90,8 @@ type Span = {
 	and the endpoint spans are always empty and at least one hour.
 */
 type Stretch = {
-	start: string,
-	end: string,
+	start: number,
+	end: number,
 	spans: Span[];
 }
 
@@ -156,9 +156,9 @@ function* edgesFromEvents(events: Iterable<ScheduleEvent>): Generator<Edge> {
 }
 
 function junctionsFromEdges(edges: Iterable<Edge>) {
-	const junctions = new Map<string, Junction>();
+	const junctions = new Map<number, Junction>();
 	for (const edge of edges) {
-		const ts = edge.slot[edge.type];
+		const ts = Date.parse(edge.slot[edge.type]);
 		const junction = junctions.get(ts);
 		if (junction) {
 			junction.edges.push(edge);
@@ -204,14 +204,11 @@ function* spansFromJunctions(
 }
 
 function createStretch(spans: Span[]): Stretch {
-	let startTs = Date.parse(spans[0].start.ts) - oneHourMs;
-	let endTs = Date.parse(spans[spans.length - 1].end.ts) + oneHourMs;
+	let start = spans[0].start.ts - oneHourMs;
+	let end = spans[spans.length - 1].end.ts + oneHourMs;
 	// Extend stretch to nearest whole hours
-	startTs = Math.floor(startTs / oneHourMs) * oneHourMs;
-	endTs = Math.ceil(endTs / oneHourMs) * oneHourMs;
-	// Convert back to ISO date string
-	let start = isoStringFromTs(startTs);
-	let end = isoStringFromTs(endTs);
+	start = Math.floor(start / oneHourMs) * oneHourMs;
+	end = Math.ceil(end / oneHourMs) * oneHourMs;
 	return {
 		spans: [
 			{
@@ -237,7 +234,7 @@ function* stretchesFromSpans(spans: Iterable<Span>, minSeparation: number): Gene
 		// Based on how spans are generated I can assume that an empty span
 		// will only occur between two spans with timeslots in them.
 		if (span.locations.size === 0
-			&& Date.parse(span.end.ts) - Date.parse(span.start.ts) >= minSeparation
+			&& span.end.ts - span.start.ts >= minSeparation
 		) {
 			yield createStretch(currentSpans);
 			currentSpans = [];
@@ -251,8 +248,8 @@ function* stretchesFromSpans(spans: Iterable<Span>, minSeparation: number): Gene
 
 /** Cuts up a span by whole hours that crosses it */
 function* cutSpansByHours(span: Span): Generator<Span> {
-	const startHour = Date.parse(span.start.ts) / oneHourMs;
-	const endHour = Date.parse(span.end.ts) / oneHourMs;
+	const startHour = span.start.ts / oneHourMs;
+	const endHour = span.end.ts / oneHourMs;
 	let currentStart = startHour;
 	let currentEnd = Math.min(Math.floor(startHour + 1), endHour);
 	if (currentEnd === endHour) {
@@ -262,22 +259,22 @@ function* cutSpansByHours(span: Span): Generator<Span> {
 
 	yield {
 		start: span.start,
-		end: { ts: isoStringFromTs(currentEnd * oneHourMs), edges: [] },
+		end: { ts: currentEnd * oneHourMs, edges: [] },
 		locations: span.locations,
 	}
 
 	currentStart = currentEnd;
 	while (++currentEnd < endHour) {
 		yield {
-			start: { ts: isoStringFromTs(currentStart * oneHourMs), edges: [] },
-			end: { ts: isoStringFromTs(currentEnd * oneHourMs), edges: [] },
+			start: { ts: currentStart * oneHourMs, edges: [] },
+			end: { ts: currentEnd * oneHourMs, edges: [] },
 			locations: span.locations,
 		}
 		currentStart += 1;
 	}
 
 	yield {
-		start: { ts: isoStringFromTs(currentStart * oneHourMs), edges: [] },
+		start: { ts: currentStart * oneHourMs, edges: [] },
 		end: span.end,
 		locations: span.locations,
 	}
@@ -322,14 +319,14 @@ function tableElementsFromStretches(
 		if (first) {
 			first = false;
 			startColumnGroup();
-			startDay(stretch.start.slice(0, 10));
-			startHour(stretch.start.slice(11, 16));
+			startDay(isoStringFromTs(stretch.start).slice(0, 10));
+			startHour(isoStringFromTs(stretch.start).slice(11, 16));
 			for(const location of locations) {
 				startLocation(location.id);
 			}
 		} else {
 			startColumnGroup("break");
-			const dayName = stretch.start.slice(0, 10)
+			const dayName = isoStringFromTs(stretch.start).slice(0, 10)
 			const lastDayHeader = dayHeaders[dayHeaders.length - 1]
 			const sameDay = dayName === lastDayHeader.content && lastDayHeader.span;
 			if (!sameDay)
@@ -343,7 +340,7 @@ function tableElementsFromStretches(
 			startColumnGroup();
 			if (!sameDay)
 				startDay(dayName);
-			startHour(stretch.start.slice(11, 16));
+			startHour(isoStringFromTs(stretch.start).slice(11, 16));
 			for(const location of locations) {
 				startLocation(location.id);
 			}
@@ -351,9 +348,8 @@ function tableElementsFromStretches(
 
 		for (const span of stretch.spans) {
 			for (const cutSpan of cutSpansByHours(span)) {
-				const startTs = Date.parse(cutSpan.start.ts);
-				const endTs = Date.parse(cutSpan.end.ts);
-				const durationMs = endTs - startTs;
+				const end = cutSpan.end.ts;
+				const durationMs = end - cutSpan.start.ts;
 
 				for (const location of locations) {
 					const rows = locationRows.get(location.id)!;
@@ -365,11 +361,11 @@ function tableElementsFromStretches(
 				}
 
 				pushColumn(durationMs / oneMinMs);
-				if (endTs % oneDayMs === 0) {
-					startDay(cutSpan.end.ts.slice(0, 10));
+				if (end % oneDayMs === 0) {
+					startDay(isoStringFromTs(cutSpan.end.ts).slice(0, 10));
 				}
-				if (endTs % oneHourMs === 0) {
-					startHour(cutSpan.end.ts.slice(11, 16));
+				if (end % oneHourMs === 0) {
+					startHour(isoStringFromTs(cutSpan.end.ts).slice(11, 16));
 				}
 			}
 		}