Due to crappy hormones, if one isn’t altered, they will smell funny to each other, and the hormones could also cause (humping and) fighting. If you are going to let them out together, then you have to keep a close eye on them in case anything starts to happen (as if you are bonding them… but if this is the case, the bonding process will probably have to start over once the little man gets neutered). With my two, before they really knew each other, (they have separate cages) I would make them take turns going for a romp. That seems like what you are suggesting? I let the buns touch noses through the cage, and sniff each other out.. but they weren’t allowed to actually be out together unless I could really monitor them closely.
Would Daisy get any more than the few hours romp at night? They should be able to ideally at least romp in the morning when you wake up, and at night before going to bed (since they have two “up” times that they are really antsy and want to run). When I was in school with my one bun, I would make sure to let her out when getting ready in the morning, and then again when I got home in the afternoon or at night. If you can do at least that, then it would be an acceptable solution, especially if you are planning on improving it with your condo!
(also note that it might take a while after he is neutered before you can reintroduce him to the other buns as well, as the hormones are all still there, and you dont want to get any buns harmed).