During these hard times... yes, I'm talking about the seriously crazy high gas prices, every little bit or tip helps. Here's one from DayTipper.com:
Best time to buy gas
Buy gas early in the morning or late in the evening on weekdays. Gas stations tend to change their prices between 10 a.m. and noon, so buy gas early morning if gas prices are on the rise. Go later in the day if prices are falling. Try not to buy gas on weekends because gas prices are often slightly higher, as stations try to profit from leisure travelers.