Depends what time you need to arrive at the airport at. If you leave the match 10 mins early to miss the traffic it takes about 20-30 mins to get to the airport I think.
Depends how early you need to check in. If it's 30-45mins for an internal flight to edinburgh then yes you should get there in time. if you've got to be there for 5.30-5.45 could be tricky.
Biggest problem is going to be getting out of the ground along with the other 30,000 who will be there (or 30,001 if Ken can tear himself away from his pool boy and sun lounger). I am sure that after witnessing the sterling performance on the telly all those armchair supporters will be flocking to the Ricoh to see this title chasing side of ours.
Living and working in Northern Ireland, I fly to the mainland frequently for business, social and pleasure: watching CCFC fits into the social side, not pleasure.
Checking in online will save time but the ability to pass through security is the important factor. And passing through security can take a lot of time, depending on the number of passengers and how moronic those pax are.
I would leave at least an hour to get through the checks. I think you are cutting it fine so you might want to book a priority ticket - I seem to recall that Birmingham offer this, most airports do.