If you want them to breed you can put them together and they will breed on the first estrus cycle. If you want to plan the kidding to a later month then you will need to separate them. Remember that the gestation length of a goat is 5 months so when planning breeding I always look at when do I want the kids born and plan back from that.
It is also important to consider that if they have been together they may have already mated. You may not observe the breeding so it is possible.