Afternoon, night or morning or half tank or whatever, the theory is similar you order a cup of hot milo, then you think the Milo is too hot causing it evaporate which you had lesser Milo in micro-litres

It is insignficantly. Just pump whenever you pass by the petrol station when your tank is lesser than half or low.

Purposely drive out to pump during morning or night time will cause you more petrol.

Did all notice whenever we pump, after the pump stop, there still would be a drop or two in the nozzle? Do you pick it up or use the straw to suck it up so that you get more petrol? <-- it could be the same theory/amount with you are getting more during night or morning. No offence.

It is insignificant, better spend those effort, time or resources concentrate on other things else like better planning on your route, servicing your car (like make sure tyre pressure is ideal for fuel efficiency), don't drive reckless like pick up then suddenly stop sharply instead slowly drive during traffic jam etc will save much much more than trying to get more petrol to pump at night or morning time.

Just my 2 cents.