Surely every domestic residence using gas is on a meter aren't they ? Not that I work in the industry or anything, but I have always assumed this to be the case. And you would need a 'fancy' meter installed, moitoring usage/times to get, say, a night rate ?
if the heating has to heat a house from cold i think it would cost more so leaving it on say 15 at night would seem reasonable. but also alot depends on how much insulation your house has a good loft and wall insulation makes a difference to the heating bills. see if you are eligable for any grants towards the cost of loft insulation etc. also try asking your gas provider for any tips on keeping warm but your bills low .
my radiators have thermostatic valves on them so i can set each radiator at a heat i want it to turn off at so i have them set to low in rooms i don't use so much ie spare bedrooms.