I didn't find the respawn rate of this area to be very fast and was only able to do it twice. Also, you can buy daedra hearts.
There's apparently a bug that if you go back in less than 7 game days they will stop respawning - happened to me and I had to buy a few to complete my Daedric set.

Easier way, buy them from the college vendor.
Make sure you enter into the buying option for Enthir
before you do anything else for the College of WInterhold.
Reason (major spoiler):
Spoiler If you don't access the vendor option from him before you become Arch Mage you'll lose it forever (or until they fix the bug) unless you do TG quests - then he's apparently always a fence.