Well, it's already been about a week and half since their neuters hasn't it? So waiting a couple weeks would put you close to the 4 weeks that it sometimes takes for the hormones to fade. It can take longer, but doesn't usually seem to take longer than the minimum 4 weeks.
I'm not as well versed on the technicalities of bonding as Lisa is, so hopefully she'll chime in. I've been lucky with pretty much being able to put my rabbits together and them being pretty ok. And I know enough about signs of aggitation and aggression in rabbits, that there are some that I won't even chance trying to bond or put together to play. Then if a rabbits behavior seems ok towards another rabbit, sometimes you just have to take a chance, and just hope there isn't an all out fight. I have several rabbits and I let them have playtime outside. Because I have so many, it makes it easier to let them play in groups, but I have to carefully pick who gets to play with who, and not all of them are neutered/spayed yet, so some boys and girls can't play together, for obvious reasons. Anyways, I got this girl bun and she was pregnant when I got her, and she had some babies. I still have most of the babies, and they are all grown up now. Well the momma bun hadn't been around the babies since I weaned them, but I wanted to be able to let her, one of her girl babies, and another girl bun, out to play together. The two girls are best of buddies, but the momma when inside playing by herself, had shown signs of aggression. So I wasn't sure I would be able to let them out to play together. So I let them see each other through a gate and they seemed ok, so I let them out together, and I was literally hovering over the momma bun with gloved hands ready to grab her up if she seemed aggressive at all. I watched for pinned ears, raised tail, but she didn't do any of that. They all just hopped around exploring and playing. But you do have to be very careful with introducing altered rabbits, and even more careful with unaltered rabbits, and just know the signs of aggression, and be ready to intervene immediately. But once you've set it up for success, like switching stuff so they get used to each others scent, then you just have to take that big step and have that first date. I don't think the litter boxes have to be completely clean. You're just trying to get them more used to being around each others scent. But you want to start with small things like food dishes and toys first. No, you don't need to wait, you can start switching those things now, then maybe after several days you could switch litter boxes. And switching play areas should be ok.
