Don't expect 72h upgrade notifications, this only occurs if there is lot's of inventory available and little demand.
The logic for the auto-upgrade is undoubtedly quite complex, on routes with YUP fares, high demand for paid and upgraded F seats and during peak travel times upgrades and inventory are held back. If your upgrade isn't cleared within the 24hr window you shouldn't loose priority to GOLD members.
The 72hr window is a courtesy, if you want to be assured of an f seat it gives you 72hrs to rebook on a flight where upgrade inventory is available, buy an f ticket, or wait out your chances.