I would say we tend to over think it as hobbyists. I have been breeding garters for many years and brumation seams to play a very limited roll in captive born and raised animals. I have had big litters, small liters, still born litters and beans at different times and under similar and different circumstances. I now prefer to just cool the animals by removing light and heat sources for a month or so. And then i just turn the lights and heat back on and introduce the males and females a day or 2 later. I always seam to be overwhelmed with babies so I must be doing something right! LOL