For the past 2 years, I put my snakes into brumation early (about a month and a half in fall of2002, and 1 month early in 2003). I did this to try to have most of the clutches hatched and feeding very well before the hatchlings were sold mid-August.
The first year, a few of the females bred and laid their clutches in accordance with the earlier schedule. However, many of them did not or produced very poor first clutches (many slugs). The second year, I had more females breed "early" but, again, quite a few simply refused all males until it was closer to the "normal" breeding season.
I regulated the temps during brumation and post-brumation to meet the "requirements, and the snakes were brumated in mostly darkness the first year. The second year, they were brumated with normal light changes for that time of year. I normally don't regulate the light cycle during brumation (difficult with my set up). I'm sure the light cycle has an important influence in the breeding season, so if you want to brumate your snakes early, keep that factor in mind.
I'm going back to the "normal" brumation times this fall since my snakes, at least, seem to prefer it.