Hi! I have fostered since Feb this year and currently have numbers 11&12 here. One was pts, the only one I had fallen for enough to want to keep, and the rest have been rehomed. The shortest time I have had them is one week and the longest 5 months.
There is no telling who will be adopted quickly really and who will need longer. I manage not to hold onto them because I have been strict with myself. I desperately want to help with the number of rabbits needing homes and if I adopt two then my ability to foster disappears. The kids are also very good, they enjoy having the fosters and do their bit to help socialise them but are also thrilled when they get a new home. As long as our own rabbits are in the garden then there's no problem saying goodbye.
My fosters are in a similar hutch to my own rabbits but don't have a permanent run as yet. They go out to a run about 10am and come in around 7pm.
The main difference to my own rabbits is the amount o time you need to spend on them. They generally need some grooming, nails clipped and handling which takes time. They also have on average four vet visits each. Two for vaccs, one pre op for their neuter and one postop. If they have ongoing health problems then they will obviously be there more often. I would say in some ways, if you work then this is one of the most important things to consider, whether you have time for multiple vet visits.
It is extremely rewarding and my rabbit knowledge has increased greatly with all the different issues I have dealt with!