But that might also be a very dangerous tactic for the once-a-day flight that with a late inbound, particularly if you have bags to check. Because the BA check-in desk will be staffed by a contract handling company and will usually still operate to the scheduled departure time and close on time. This is because the check-in staff will be contracted to other airlines throughout the day so they will close at the scheduled cut-off time.
I fly BA to GOA regularly and this is only a once-a-day service. 4 people missed their GOA-LGW flight last year by doing just what you said you may do; they saw the inbound was 3-4 hours late and thought they would have an extra few hours sightseeing. They turned up later (with large bags to check after being on a cruise for 2 weeks) and found no BA check-in desks open and nowhere / no one to accept their bags as the desks still had closed on-time to the original flight schedule. An expensive lesson for them too, just like the OP
Agree. But this is where you might use experience to play it by ear. If check in normally opens three hours before scheduled departure, and closes 45 minutes before scheduled departure... if you
know your inbound is 4 hours late (flightaware) you might aim to get to the airport at the checkin cut off... just 45 minutes before the scheduled departure. This can save you at least 2 hours of hanging around the airport.