Well, there's no real "exact" amount of time, and it can also depend heavily on what part of the country you live in as well. Most breeders like to let the natural temps in the area dictate when they brumate. But in addition to "cooling" them, it can also play a handy part with people with moderate to large collections in not having to feed them. This can be a real money saver, as well as time spent cleaning up after them, etc...
Where I live(central Florida), I start cooling them around mid December, and let them start warming back up around March or so, depending on if I think cold fronts will stay at bay. And if there should be a few stray fronts after that, I just break-out my space heater and set the temps to around 79-83 until the outside weather consistantly stays around that temp. Like I said, different people from different parts of the country, or even the world will do things differently, but this seems to work good for me where I am at.
Generally, a brumation time of 1-1/2 to 2-1/2 months is the norm, sometimes even longer, at temps of 55-65 degrees, but sometimes even much less of a brumation time will work many times, it's sort of a what works for you and the snake's thing. I think yours will do okay, if they are cooled for a month like you say, and slowly warm & feed them afterwards, they will probably just breed a little later than they normally might otherwise.
A key factor for the female being ready to breed and being receptive, is her post brumation shed, this shed tends to coincide with her follicle production, and usually has an underlying pheromone smell after the shed is sloughed that the males find irresistible.
good luck!, ~Doug

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"Better to be silent and thought a fool, than to open mouth and remove any doubt!"