Ambassador, British Airways; FlyerTalk Posting Legend
Join Date: Apr 2012
Location: Leeds, UK
Programs: BA GGL/CCR, GfL, HH Diamond
Posts: 42,997
Standard practice for BA short haul announcements seem to be as soon as doors are closed (about 10 minutes before departure), just after or some point during descent (around 20 minutes usually), 10 minute call, and finally parked on stand.
I imagine BA pilots (as with most pilots), are able to judge whether they have the time and "bandwidth" at any particular point during a flight to make an announcement.