How to make repeating doodles?

Question

JavaScript

The task, it seems, is trivial - a slightly extended functionality of the to-do list) The solution is not so obvious.

Interested in the best way to implement. Case: the user sets the repetition interval in his task, at which time a new record is simply created in the database.

What are the options? So far, only crowns come to mind, but then I get lost. It is clear that the approach is different if this is one tushka, and if there are a thousand / ten thousand / million. Interested in a highly loaded version, or simply the most scalable. I would be grateful for any poke nose in the right material)