The normal time is about 2 hours before the flight, but with the new passport checks, I would allow at least an extra hour. I would plan on being there no later than 9-9:30am.
I try to discourage people from coming to the airport from long distances like this due to the uncertainty on the roads. An accident, a mudslide, construction, or general traffic can really mess up your plans.
I suggest you come in the day/night before, and stay in SJ overnight and leave for the airport at 8:15am. There is a daily Interbus shuttle at 10am that arrives in San Jose at 12:45pm. It's $37.
http://www.shuttlebus.co.cr/website/sho ... /index.php