IF I saw a 5 or 10 hour delay on the app I would probably phone and ask if I could go later to the airport

The BA app can be quite primitive, a flight with a length delay today into heathrow could result in the app showing a lengthy delay for your flight tomorrow, as the app does not consider that the aircraft will over night in heathrow and so could make up time.

Typical advice, not only from BA, is to get to the airport for the scheduled departure time. I have had the exact same with LOT, and email at 9am telling me my afternoon flight was delayed 2 hours. When I called and asked I was advised to get to the airport on time as there was nothing on the email saying I should come late.