Normally the towncar service will suggest a pick-up time. For a 10:30am flight they will probably suggest between 8-8:30am for pick-up. MCO gets really busy and the lines get long at the security check point so you probably don't want to get there later than 9:00am.
However, if you must stop at your airline counter first please allow more time. When we arrived at MCO on a Saturday afternoon in late June the line for the counter was HUGE!
Although we already picked our seats on-line on the AirTran web site we didn't have a printer available to print out our boarding passes like we did for the trip to Orlando.