None. Baby "bonds" don't count. It will always be a hit or miss as to whether or not two young rabbits will bond.
The best way to have a bonded pair is to get an already bonded
and fixed pair. There are many adorable pairs available from rescues. Getting young rabbits is just not your best option. I realize most new owners-to-be assume that it is best to get young ones so they can bond with them, but rabbits are not like dogs in that regard. In fact, adult rabbits (6 months and up) are recommended for first-time owners because they are sooooo much easier to care for.
With a fixed rabbit, you get to skip the messy, mushy poo stage, the hormonal stage, the high cost (and worry) of spay surgery, the stress of the bonding process once both rabbits are fixed and have had several weeks (minimum) apart and caged separately. And you skip the possibility that the two rabbits just won't bond (in which case you'd be stuck housing both separately, exercising both separately and twice the work).
Possible hormonal signs can include grumpiness, forgetting potty habits, growling, lunging, biting and spraying urine.
There were a couple recent RO members who asked a similar question as you. They were given the same advice (by others) that I just gave. And then they still opted for the babies. Several months later, they admitted that they now wished they had listened and regret that they did not heed that advice.
If you'd like further information on this subject and generally on keeping rabbits as indoor pets, check
here.
