I have dwarves, so I treat them differently, I find they're most comfortable coming out for shorter periods, I don't have a ball for them, as I think they can just as easily run in their wheel..I let them walk around my room, but keep a close eye on them at all times, and don't let them go behind anything. I get them out often more than once a night, but they seem to prefer being out for little bursts.
I know whoopi is a syrian, and therefore different..but that is an avenue you could explore..maybe..10 minutes at night and 10 early morning..or something.
Half an hour sounds good
and you're right to give her rests (mine like to have a snack
)