I got a text a good 20 hours or so before AA1667's scheduled departure at 7:47am on 12/21/2022, that the flight has been delayed precisely one hour. No other AA flights seem to be impacted.

By sheer coincidence I had scheduled a callback from AA for some other matters and so I talked to an AAgent an hour later. He said "crew availability" was the cause.

Just curious what this might be about. A very specific condition, say, a crew member calling in sick and after a scramble, a replacement was located? Or something more general, in which case the new "estimated time" really is just an estimate, and I might be in for a very long day...?

Basically wondering how reliable a new time may be for a pre-announced, crew-related delay...