You will see the "evidence" stuck all over the does tail and back end if the buck bred her. I put my buck in with my "to be bred" girls 150 days from the earliest date I want kids and leave him with them until they come inside for the winter. My goats cannot go outside in the winter because the snow totally fills up their outside pen and the gate freezes shut (or open). They are also in the barn when I am not home. The buck has a separate inside stall, but during breeding season he will share their outside pen. They are usually inside for the winter by December, so the buck is out with them for 2-3 months.
However, I check back ends and mark down who got bred when, so I know when to re-check for heats. My girls are all pretty obvious when they are in heat, so I also mark that down on the calendar. The buck stall and outside pen both share a wall/fence line with the does, so it's easy to see who he is extra interested in and which girl is flirting hot and heavy with him. I have a very small place, so I am in sight of my goats all the time i am home and awake. Its easier for me to observe them than if I had a large pasture. As much as I would LOVE to have a bigger farm, sometimes smaller is better.
The heat cycle depends on the doe I think. I have had does suddenly come into an off-schedule heat when a stinky buck arrives and there is suddenly a buck on the property, others don't care and continue with their regular cycle.
DragonLair Farm in Central Maine. Nubian, Lamancha and Oberhasli dairy goats, 3 horses, 10 dogs, 2 cats, 5 Guinea fowl and not sure how many chickens.