You could go figure out the exact minimum amount of time that you need to spend resting and staying sane, but the effort to do this would also burn you out, so you need to go take a break from that. And you could go stress out about how much rest you need to be able to go back to thinking about how much time you need to spend to rest, but this too will burn you out, so you need to take a break from that.

And this will continues to apply to however many meta-levels of stuff to stress out about you invent, so go outside.