"If you’re currently on a 6-month recurring subscription with a future renewal date, you’ll receive Sapphire Skyblazer as a gift in your Battle.net desktop app at no additional charge no later than July 13, 2021 (must be redeemed by December 31, 2021)."
https://us.shop.battle.net/en-us/pro...t-subscription
It says that on the subscription page. I've had to wait two days a few times but the rest were always same day as announcement. I still haven't got it yet.