feat: Convert helpers to use JS files

packages/backend/src/helpers/delay-until-as-milliseconds.js

@@ -0,0 +1,8 @@
+const delayUntilAsMilliseconds = (delayUntil) => {
+  const delayUntilDate = new Date(delayUntil);
+  const now = new Date();
+
+  return delayUntilDate.getTime() - now.getTime();
+};
+
+export default delayUntilAsMilliseconds;