I arrived at the airport an hour earlier than expected. The staff at National were accommodating and allowed me to pick up the car an hour earlier. However, the free GPS provided by QEEQ did not work, causing me to get lost in Bangkok. On the return day, I got back ten minutes later than the expected return time and couldn't fill up the tank completely (it was one notch below full, and I estimate it would cost around 100 THB to fill it up). National charged an extra 450 THB, but I am not sure if it was for the fuel or the delay.