It’s not uncommon for there to be disproportionate grooming in a bonded pair. I’ve read about (and also currently have) pairs where essentially only one rabbit grooms the other, and that’s how the hierarchy was established.
I personally would say move forward, and if you see signs it’s not going well, remember you can always go back! It’s hard for people who aren’t actually involved in the bonding process to provide guidance, because ultimately every bonding process is different because every pair of rabbits is different. It sounds like you have a good foundation so far, and you’ll only know if you can go farther until you try. It seems like the likelihood of an instant fight is quite small, so it seems like a safe time to try longer than 8hrs (with you supervising) and/or expanding the area a bit to give them more room.
The answers provided in this discussion are for general guideline purposes only. The information is not intended to diagnose or treat your pet. Seek the advice of your veterinarian or a qualified behaviorist.