According to deer researcher and writer T.R. Michels, although bucks may begin rubbing as soon as they shed velvet, as early as September 1, they often go through what he calls the "Dispersal Phase" in some areas, which is when they move from their summerhome ranges to their fall home ranges, and when the older bucks begin establishing their breeding ranges, making rubs and scrapes along their semi-regular used (daily) travel routes.This oftenbegins about mid-October in the upper midwest, and earlier in the south. So - you can look for rub routes in September, but you may have to look for them again after mid October.
Check his "Deer Activity Graphs" at
www.TRMichels.com