For anyone else curious, my reasons for the big change in chat message date handling, in no particular order:

Ease of finding out the date of a message if many occurred on the same date (the [ D sequence is new).

Annoyance at the JAWS stutter on navigating across a date boundary in older scripts. This was caused by my
having to navigate, abort the default announcement, announce the date, and then re-do the normal message
announcement.

Annoyance at having to wait through full dates before I could hear a message's content, especially in
conversations where most days consisted of only one or two messages.

A few users over time commenting that they were confused by my "Leaving ..." announcements.