I'm predicting (from past experience) that I will not be able to get a BP online so will have to get that at the airport. I have a meeting in central London which may mean I might only get to LHR around 75 mins before departure at 2025 -- that's 15 mins before their minimum checkin time of 60 mins. But I'd prefer to get my BP earlier in the day and then go back to central London for my meeting so I only have to clear security and get to the gate later on. So the question is what's the earliest I can get a BP at LHR? There's an earlier flight at 1740, so presumably I could get a BP around 3 hours before that at 1440? According to CA's web site there are also self checkin machines which operate up to 5 hours before a flight (which would be 1520 for my flight or 1240 for the 1740 flight). Will I be able to use those? Do they usually work? I'll be hand baggage only so just need that BP. I've tried ringing CA but couldn't get a definitive answer... Thanks.

PS If it makes a difference my ticket was booked with an OTA rather direct with CA owing to a massive fare difference, and I'm flying in J.