We are flying from Dublin to Edinburgh Scotland on a 6:40 a.m. flight on a Tuesday in June. How early should we arrive at the airport? Thanks!

Aer Lingus recommends 2.5 hrs before departure, check in closes 45 minutes before departure.
You might get away with 90 mins before departure that early in the day if you want to take a risk.
Personally I go with what the airline recommends - the extra hour in bed is not important enough to risk missing the flight because of problems getting to the airport etc but I'm risk averse.
Edited: 5:35 pm, February 02, 2013We plan to actually check-in online 2 weeks prior to our flight. I just wonder what time to physically be at the airport, if we have already checked in and printed our boarding passes at home. Thanks!
At that time of year it's busy and you still have to check your bag. If I were you, I'd be there two hours prior to flight minimum.
2 hours in advance particularly if you are not familiar with Dublin Airport
Thanks, everyone -- we will plan on at least 2 hours then.
I agree, it is early so should be quicker at security etc but i would still get there 2 hours earlier.