My experience of Manchester airport is that the security procedures took forever - but that was international and the domestic side may be better. In principle you should think in the following terms: If the check-in closes 40 minutes before departure, and it takes 10 minutes to walk (quickly and non-stop, no perusing of shops, etc.) to the gate from the far side of security, then so far you should check in 40 minutes before scheduled departure (the gate will close 20-30 minutes before departure). Remember that you must allow for getting to a check-in (front of queue) where other flights may be checking in - the desk may not be dedicated to only your flight. For this add 10 minutes minimum (you are now up to 50 minutes). Security can take as much as 15 minutes on a good day, 25 minutes on a bad one, and you must allow for this (you are now up to, say, 75 minutes). Allow a further 10 minutes for contingency (finding the right place to check in, toilet stop, search for documents, etc.) and you approach needing to aim for entering the terminal one and a half hours before scheduled departure - you will not have much unavoidable waiting time there even if everything goes very smoothly (40 minutes at most if you are the only person in the terminal, I would think). Airlines routinely recommend/insist you arrive at the terminal 2-3 hours before departure.