When we breed our girls, we let them 'hook-up' twice over a 3 day period. For instance, if we get them together on a Monday, we wait to do it again on Wednesday. It's always worked. (Just one time on each of those days.) I like the males to be at least 1 1/2 yrs old. Note: And they usually throw 4 pups. So don't make the mistake of thinking if you breed them more often, you'll get more pups.
Good luck!