18-21 for each faction takes quite a bit. The first time you beat a Crypt you are restarting every time a champ dies, playing a lot of RNG roulette, playing stun set roulette, hoping you get things like 75% sleeps or TM reductions to work, etc.....
Finishing 2 crypts in one day is a big task, and required looking ahead, planning, farming food to rank champs up, and farming silver. Most of the time I would finish one the night after reset, then the other be struggling to finish by reset again....but usually you are ticking off only one per reset, and a few each week in total.
If you're opening up all the crypts to make some general progress and collect forge mats to fore perception,especially during a CvC where you are resource light and can't just run spider/dungeons/tag, that's good stuff.