what time of day do IPv6 privacy addresses usually rotate on Apple devices?

iOS and macOS long ago implemented support for the privacy extensions of IPv6 networking, iOS in version 4.3 and macOS in version 10.7. The Apple document IPv6 security says in part that temporary addresses have a lifetime of 24 hours. My question is, how is the expiry time chosen? Is it at multiples of 24 hours after the last boot? Or it is tied to the local timezone (and happens overnight)? Or is it at random, with some jitter from a 24-hour schedule? Or something else?