Temperature seem to play a big role in production time for flies. In late spring through early fall, my home temps are in the low 70's, and my fly production time is about 7 days for melanogaster and 4 weeks (or a little less) for hydei (that's start date to first new flies). Those dates seem to shift when the house temps get lower in the late fall/early winter. I actually placed a waterbed heater with a towel over the top in my ff cabinet to raise the temps a bit in there. It took some experimenting with the proper temperature setting, but works quite well.