While we know iOS 15 is coming on September 20, Apple has not specified exactly what time of day it will be released.
In some parts of the world, this corresponds to times early in the morning of the following day, and Apple's regional websites for some of these countries do list the release date as September 21 rather than September 20.
Pacific Time on Monday, September 20.
watchOS 8 can be installed on Apple Watch Series 3, Series 4, Series 5, and Series 6 models, as well as the Apple Watch SE.It is not compatible with the original first-generation Apple Watch, Apple Watch Series 1, or Apple Watch Series 2?
When Apple released iOS 14.5 in April, it introduced the ability to unlock your iPhone with Face ID while wearing a mask, as long as you are wearing an Apple Watch.