Thank you @Blue eyes ! I'll admit, I am a little afraid that Ellie may not take to him very well. But fingers crossed and lots of patience on my end hopefully will helpI would say a minimum of 2 weeks in the side-by-side pens in the 'other' neutral territory. You will probably be the best one to make that determination as you observe them over the 2 weeks.
The immersion method time can vary wildly. I would be reading over the following link (again and again -- that's me, anyway):
You'll want to be ultra sure they are bonded well in that secondary neutral space before moving them into her old territory.INTRODUCTION TO BONDING METHODS Most rabbits are territorial by nature. However, this does not mean that they have to lead solitary lives. Rabbits that live in compatible pairs or occasionally even small groups will benefit in many ways, including companionship, mental and physical stimulation...cottontails-rescue.org.uk
Since @EllieBelle is also about to start bonding, just wanted to mention that the two of you may have similar or may have polar opposite experiences with bonding. It really can be so incredibly different per rabbit and per bond. All the best laid plans may not prevent two rabbits from refusing to bond. So neither of you should feel like you're doing something wrong if things don't go as smoothly as it may with the other.
I've had the experience where 2 rabbits were instantly bonded the first day with no effort on my part. I've also had some that refused to bond (and some in between). So one never knows until everything is in process.