Things are pretty quiet all around on a Sunday morning. I would allow sufficient time for the drive down from Santa Fe in case there's an unexpected delay on the road like construction or an accident. Other than that, transit from the car rental depot and security are generally pretty fast. As mentioned above, there's no obvious gas at the main airport exit-- but there are plenty of stations within a mile or two. Map it out ahead of time so you don't have to spend 15 minutes driving around looking.