Is it possible to let rats out of their cage to explore TOO much?

I'm a pretty busy person, so *usually* I can let my boys out for 1 hour per day, but sometimes this just doesn't happen (if I'm not home). My parents will talk to them and pet them and hold them sometimes, but for 1-2 days (very infrequently) sometimes they don't get to run around my room. So then, when I get back, I'll let them out and allow them to run around my room for 2-3 hours at a time. They usually end up sleeping on paper "nests" they make under my bed. I'm just wondering...is this bad? I feel like an awful pet owner when I miss a day with them, but sometimes it just can't be helped. I do feed them fruits and veggies 4-5 times a week, little bits and pieces here and there and sometimes whole mini salads. :) I give them lots of love and attention when I'm there, and they both know their names and the word “treat” ;) Soo.. I'm just wondering, is this okay sometimes? I really love them and it's infrequent that they don't get to come out and play, but I feel awful when it happens.. :(