It was my understanding that the red anticols are turned on as soon as the aircraft's hydraulics are powered... at least this was my experience during my maintenance work (767s, MD11s) where it would be done inside the hangar to warn the personnel working there to keep clear of the landing gear, flaps and other bits that have the potential to mangle people simply by pulling a lever on the flightdeck.
So am I correct in assuming during normal operations it's done only when the first engine starts spooling up during or after pushback (the hyd demand pumps already powered)?