In my link above, it's pointed out that higher temperature "may" increase the size of the pumping volume in the pump; and since it's more susceptible to air temperature changes than the buried gas reservoir, that'd mean you get more gas when you pump during the day! :BLAA:Its old news that filling up when its cold, yes I'm sure it "helps" get you a very minuscule amount more of gas but in reality since we do not live in areas were subterranean tanks would have a temperature difference of 30-40 degrees it makes the change in temperature negligible.
For you to have any sort of monetary savings you would have to live in an area that is 100+ during the day and <30 over night. On top of that to make it worth it you would more than likely have to purchase 20-30 gallons.
The people that operate gas stations may not be smart but those who own them are, and if there was really a difference they would find a way to adjust it to reduce any benefit for the consumer.