Check-in times vary by airline and airport. Most airlines now require passengers to be on board the aircraft 20 minutes prior to departure for domestic flights and 30 minutes to an hour prior to departure for international to accommodate required 'positive baggage match.'
Don't forget that you'll have to:
- Park your car - somedays it can take forever!
- Get your boarding pass and register your luggages
- Pass the security check
In my case I like to arrive 2 hours before the flight and drink a coffee waiting rather than arrive at a closed gate,