To accomplished this via scale to zero, New feature: Scheduled machines is a good place to get started, but you can’t run it at a specific time.
If you want to run at a specific time you’ll have to keep a machine running that runs something like superchronic as outlined at Recurring scheduled tasks (like cron) - #25 by Brad, but you can’t achieve “scale to zero”.
There’s no perfect answer at the moment, but at least you can choose between the trade-offs of cost vs accuracy.