there used to be a significant problem coming out of covid where the gate lead would change it to gate open when they arrived (around 60mins) but not advance the status to boarding when they started around 30 minutes. you can board a flight with the status as gate open, but to actually close a gate you do need to advance thro boarding/final boarding/gate closing/gate closed. you would therefore see the status as gate open for ages, then fly thro the other statuses within 1-2 minutes. it happens a lot less now thankfully. a sign this is what is happening is if the flight is still showing as an on time departure in the ba app, but still showing as gate open at 25-20 minutes to go, at that point you should go to the gate as it is probably boarding. it is always a good idea to also use the LHR and BA app as well to check on gate and status.

this is not an attempt to blame the OP in anyway, just some context and background.