They can be solid breeders for 6 months and sometimes up to a year (1.5 years old).

They are pregnant for 3 - 4 weeks then with the babies for another 3 - 4 weeks, then back to pregnant. That's why you do colonies. 1.2 or 1.3 or 1.4

Just remember the larger the colony the more you may need to separate the mothers out, some people will leave the females in with the males after they give birth. I separate mine out, but just recently found out not to put two nursing females together. They fought and one litter ended up getting killed.