Letting your rabbits have the winter off is very much dependent on where you are geographically. As I am in Texas, which is rather warm during the late spring through early fall, my breeding time is limited to late fall, winter and early spring.
Bucks go temporarily sterile in high temperatures. Please keep that in mind. If your hot temperatures are 85 and above your boys are shooting blanks until the weather cools down AND stays cool. Rabbits are remarkable well suited for cold weather especially if you keep cold wind off of them.
Another thought that I don't think came up in this discussion is I think I read that you are wanting to leave a buck in a colony full time. I don't think this is a good idea as the does may not want the buck pestering the does whenever he gets the notion. I don't have a colony set up so I may be speaking through my hat, but that is what I have read from several sources. I do know that bucks will try to breed even when the doe is not in the mood.