It's when the bees top moving old wax around and start making new wax. Usually just before the main flow. But you can get some earlier if you put empty frames in the brood nest.
OK this is probably a silly question. Michael you said "when the bees stop moving old wax around..."..do the bees reuse wax in their hive? Like I guess when they are rebuilding the comb that may have been damaged by extracting honey. Do they reuse this wax, if so, how on earth do they do it? do they chew it up and put it to rebuild? Great day. Cindi