Here's the deal: Yes, your metabolism affects your size, and the faster your personal motor runs, the more calories you'll burn. But the truth is, a slow metabolism isn't the real reason you're packing on pounds. You are the reason.
As a general rule, arrive at the airport no later than two hours before your domestic flight is scheduled to depart. This is somewhat later than the typical suggestion of three hours for an international flight.
It is recommended that if you are flying domestic, you arrive at the airport two hours prior to your departure. If you are flying international, a lot of airlines suggest that you arrive three hours prior to your departure time. Personally, because it's that early in the morning, I'd be at the airport about an hour and a half before your flight leaves (if you're flying domestic).