Fix 'install now' click after download

ts/util/timestamp.ts

@@ -8,3 +8,11 @@ export function isMoreRecentThan(timestamp: number, delta: number): boolean {
 export function isOlderThan(timestamp: number, delta: number): boolean {
   return timestamp <= Date.now() - delta;
 }
+
+export function isInPast(timestamp: number): boolean {
+  return isOlderThan(timestamp, 0);
+}
+
+export function isInFuture(timestamp: number): boolean {
+  return isMoreRecentThan(timestamp, 0);
+}