I think it's safe to say he's not fertile anymore; however if you want to be on the extra safe side wait another couple weeks.
I introduced Mango to Maia only one week after he was neutered, but she was already spayed. However, he did try to hump her for a while and only after he stopped did they become friends.
So if your rabbit still tends to hump his partner (in a sexual way and not as a display of dominance), wait a little while more.