Any help on this matter greatly apprecaited

We have just moved into a 3 storey house , that has gas central heating boiler.

What is the ideal temp in 0c to operate this to heat the house.

weve been told different things by people we know , but im still unsure.

I think that around 75 or 80c is right , yet someone else says 50c

also what would be ideal times for setting heating to ?? is is ideal to have it on for say 2 hrs in am , and 2 hours at night , does that use up more gas, or have it on for longer

Any advice??

Simon