GasBuddy.com did a study on the best time to buy gasoline in each state. Friday afternoon is NEVER the best time...
This study is all about pricing. Generally, Monday mornings (or Tuesdays) are good, before gas prices change for the week. The WORST day to buy gas is Friday, because that's when gas stations bump their prices up to make more money off people leaving town for the weekend.
If you're in Alabama and Mississippi....fill 'er up on Tuesdays and Saturdays. Florida? Mondays and Thursdays. Get the list HERE