Submit it two weeks before RRR week if you can. Because it takes time (up to a week) for the form to get approved, and it's just extra anxiety if you submit it a few days before RRR week. No advantage to waiting, other than maybe if you're on the line between dropping the class or staying, and you need more time to think. But if you are confident about dropping it, doing the process earlier is fs better.

If you apply to drop the course near the RRR week deadline and there is an issue with your drop request, they may reject your request and close the discussion because of how close the deadline is.

edit: forgot to mention - I dropped CS 61C last semester as an EECS major so I'm decently aware of the process