I am not sure whether you actually mean night or evening
Both use the same source of fuel. Your central heating you can control via thermostat/s and a timer, such that if you wanted it on at night whilst asleep that's possible. It isn't normally possible to do that with a gas fire, and from a safety aspect, gas fires have more risk attached than boilers in general. Assuming the CH is fairly recent you should have TRV's on the radiators which allows you to control them individually. The system should also be designed to heat the whole house if needed in a planned way,something the gas fire isn't really meant to do
That said if it's evening and you want instant warmth and are sitting close by the gas fire, it may have some advantages over CH
Not exactly sure of why you want to heat the house if it is during the night, but if it's as usual to heat the house prior to getting up then a few hours before will give a better result than say just after midnight.
If you want instant heat and are sat in front of a gas fire, fine, if its to heat the house during the night reasonably uniformly in a controlled way, then CH.
