I cannot speak for breeders but, I have had to reset the clock as it were because of an unplanned acquisition and I wasn't happy about it. Especially, since I was already 2 months into the 1st QT.
My new solution has been to take over a small space in other rooms and just get more snake tools as needed..
But, I would imagine that larger breeders have done something similar with several QT areas or restrict themselves to larger, less frequent acquisitions. Well, at least the breeders that I consider "the good guys" i.e. responsible enthusiasts with a real passion for the animals they deal in.