Arty, the answer to your question depends on your region and amount of daylight....shortened daylight hours, stimulates an increase in testosterone levels, which in turn reduces the blood flow to the velvet....that is when antler growth ceases, and the velvet begins the dying and drying process, and hard antler begins to form....whatever rack he has got at that point is the rack he will have, until he sheds his rack, or breaks it off, fighting during the rut
Again, depending on your region, velvet growth generally ceases, during mid-August to late September.