Schedule Firebase function at specific date/time

In my app users can create an event which can be started immediately or some time later (max 5 days). How can I schedule a Firebase function "StartEvent" at the exact date that the user wants it?

I already tried it with the Node plugin "Node-Schedule" but it seems like Firebase is removing the stored schedule after a certain amount of time.

My other idea would be to set up a cron job on an online service that pings a function every 30 to 60 seconds that checks if an event must be started. But this seems very inefficient to me.

Is there a better way to do this?

via sunilson