The shortest period at all is two days, the gap between macOS 13.2.1 and macOS 11.7.4. The shortest time period between any two releases in the same OS generation is six days, which is how quickly the 10.15.5 Supplemental Update 1 came out after the 10.15.5 release.So on average, we've seen some sort of update every 44 days. As of Febru(11.7.4's release date), it's been 8190 days since the Public Beta was released.This version was only for the then-new PowerMac G5 and the flat panel iMac G4, and was never generally released. This figure includes the one odd macOS X release: 10.2.7. Starting with the Public Beta and up through 11.7.4, there have been 186 macOS releases, both major and minor.

Some random notes, updated from the original post: This has happened a few times over the years. This is to keep the version numbers in the proper order, even when an older OS received an update after a major new release came out. Some entries may appear out of chronological order (i.e. Note: The Days column reflects the number of days between releases. Ⓘ Leopard - First universal binary release Ⓘ Snow Leopard - First Intel-only release Ⓘ Lion - App Store only (USB stick later) Ⓘ Ventura (Taxes were too high in Santa Barbara?)

How to upgrade mac 10.7.5