Do I get more petrol (gas) if I refuel my car at night or do I get more of it if I refuel during the day?

If the weather is colder, the volume of a certain mass of petrol is smaller, so you get more for your money at night (provided the night is colder).

This assumes that the petrol pumps measure volume to determine amount.
The amount of energy produced depends on the mass.

I think at night
Cz the nights r comparatively cooler than days

I don't think there would be much of a difference, as most gas stations keep the fuel at a constant temperature while it's in storage. Usually 15 degrees celsius or so.

They keep it in a tank in the ground, which is cooler at night :p, they don't monitor temperature or anything.

I think it makes a difference ,may be 1 or 5 % but it does make.