Reply #7: The "fill up in the morning" thing is mostly bs. As stated here, the tanks are underground.

[yellowcanine]

Therefore the gasoline in them is influenced very little by air temperature. The amount of exposure to air temperature during the pumping process is minimal also, so the change in density is going to be minimal as well. You are going to save more by filling up at a gas station on your daily commute that gives you the best price per gallon, regardless of what time of the day you do it. So stick to the routine that allows you to fill up for the cheapest price.