Question about exercise for my guinea pig/hamsters?

[Claire]

I have a guinea pig (soon to be 2 guinea pigs) who is 3 years old, and I know I've asked this question a lot, but I want to know exactly how long I should let her run around. She has a giant exercise pen, set up with blankets and towels down, tunnels, paper bags with hay, stools for running under, places to hide, and then to encourage her, I give her her veggies all spread out over the space. When I let her run around, in the evening, she goes and get's all her favorite veggies, which only takes her about 20 min, and then she just finds a cozy bag, and sits there lazily for the rest of the time. So should I let her just run around for 1/2 hour, since that's the time she's actually active, or and hour plus, and just let her relax there? Then, it's a similar situation with my hamsters. They run around for about 10-15 minutes, and then they just find a place to fall asleep. Should I only let them run for that long, or the whole hour, and just let them sleep? Also, is it okay to let them run around in the same pen as my guinea pig (not at the same time)? Thanks in advance!