Petrol expands when it gets warmer and is generally stored in tanks underground, so it makes sense to fill up early in the morning when the ground temperature is still cold.
That way you can be sure that your litre is actually a litre. The colder the ground the denser the fuel.
Be careful filling up while a tanker is pumping fuel into the storage tanks, any dirt settled on the bottom can get stirred up and be picked up into your tank. It might be a good idea to wait.
When towing you use approximately 3O% more fuel doing 1OO - 11O kilometres per hour as opposed to 9O - 95 kilometres per hour.