I have used “fast-track” bonding marathons when bonding my fourth and fifth into their group. I will advise you it can get very stressful. And there’s no guaranteed that will bond them either. (Beware, you may not get much sleep!) I have some experience with bunny bonding – and as Beka suggested this is typically only used after your buns have had smaller dates.
With my last addition – Nora – she had about 4 dates with the other bunnies – the first date was about 20-30 minutes and the next three were about 5 hours of her remaining with them – before I had a bonding marathon and she was bonded. It took about 3-4 days of them being together non-stop before I deemed them “bonded”. But I also should tell you that I’m very familiar (being on my fifth addition) how each of my rabbits reacts to a new addition. When I bonded my fourth into the group, Simba, I did about three weeks of initial dates before doing a bonding marathon where they were together non-stop until bonded. The only way I was able to do this marathon bonding is simply because I have become very used to their reactions to new bunnies and how they bond as a group most successfully. I STRONGLY encourage you to become familiar with their reactions to each other in different situations before attempting this.
Also, with marathon bonding – I’ve had the most success with starting them at different levels throughout the bonding before moving them. Before I did marathoning, they could sit still in the box (cuddling – they didn’t have much room so they were usually always touching) for at least a half hour with no arguments. They remained in the box for the first 7 hours of my marathoning with nothing but hay and water – so no one could fight over literally anything. The box has always worked well for me because it forces them together with lots of interaction but is a more controlled place where I can easily stress them out if any fighting got out of hand. After the 7 hours, I moved them to a very small x pen with food, litter boxes, and water but not much room to chase. Chasing did happen. It always did every time I moved to another area. Once they had mastered being in that area together with only a few bickerments and absolutely no full-blown fighting I made the x pen larger. After the same thing happened, then I finally put them in their area they would live in together. As you can see, it’s really a stepping stone process and if your buns are not ready to move on to the next point, they most likely won’t. They have to be ready or you’ll just be inhibiting their relationship. This is why smaller bonding sessions first can be so necessary.
Here’s some links to my rabbit blog – I’ve created some articles about bonding that may interest/help!
http://www.wheekwheekthump.com/category/bonding/
Not sure if this is allowed, Beka! Feel free to remove the link if not (idk if it’s considered promoting another site or not?). Just thought one of those articles may help if she is interested in different opinions and ways of bonding!