It varies from person to person, and depends on when your females start ovulating. Mine started in January. I also know people that were getting eggs all through December.
"Ovulating" is when the female gecko starts to make eggs. That has to happen before the mating will do any good. There are pictures of ovulating geckos (you can see it through the belly) on the forum if you do a search. Once the eggs start to form, they can be fertilized by the male.
Are you just interested in finding out more about breeding, or are you thinking of trying it with your geckos?