I just started the breeding attempt a month or so back. I'm using 3 sterilite shoebox tubs.
It took a couple weeks for the mealworms to pupate, and a couple more to turn into beetles. I've got a lot at all 3 stages now, but no new larva noticed as of yet. I've had the earliest beetles for 2 weeks now I think.

The majority seem to be in pupal stage right now.