At those ages, hormones can start at any moment. There is really no benefit to even attempting to bond them before they have been fixed. It won't make bonding after surgery any easier since they will both smell different and be different once they return from surgery. Plus they have to stay apart for several weeks after surgery anyway -- again, that would negate any 'togetherness' they may have had prior.
However, attempting to put them together now (before surgery) does run the risk of destroying or hurting bond attempts later. If they happen to start fighting now, that could carry over to animosity later on when the real bonding begins.
Your best and safest option is to keep the rabbits completely apart now. Save the bonding for after their surgeries are complete and they have had time to heal. It can take 4-8 weeks after a neuter for those hormones to fully dissipate from your buck. He is old enough to neuter now, so you can get him scheduled already. The female can be scheduled (depending on your vet) at around 5-6 months of age.
