We flew US Air in May but we had a 10:20 flight. When I called the airline to ask how early to arrive they told us an hour and a half. We only waited in line about 10-15 minutes before we were through security. We had a lot of time before our flight after security but with the time of day that you are leaving it may take a little longer to get through the lines. Good luck--hope this helped some. If all else fails, call your airline and ask.
We had an 8am flight in June, arrived at the airport at 7, breezed through security and had time to spare. It was a Sunday morning, however. I don't know if this makes a difference.
We had an 8:00 flight on United 3 weeks ago and arrived about 6:30 a.m. We were basically "waved through" security (can't say I was very impressed with MCO security checks at all-I guess we looked like the innocent family we are) and then had time to do some last minute shopping in the Disney store there before our flight.