FLR- Duty hours...
I don't think anyone in Longhaul at BA tracks their duty hours, they're more interested in Flying hours and/or days away from home, so as Sygyzy has said I doubt anybody can answer your question.
FWIW a
average longhaul month might involve 18-20 "working days", ( just to be clear I'm counting any day that is impinged upon by work as a "working day", so a trip that leaves LHR late on a Monday and gets back early AM the following Wednesday is a three day trip). That month might be made up of say 6 X three day trips
or 4 X 5 days trips - all depends on the bidline gods. No Airport standby or standby downroute at all in longhaul and Home Standby is only done as part of a pre-allocated Reserve Month ( comes round every couple of years). Simples.
There's also the ability to flex the months up and down to a certain extent - work light one month ( e.g. one three day trip less), harder the next ( e.g. one trip more), though the amount of flexibility you'll have would depend to a great degree on your seniority.
Sorry if that doesn't answer your specific query about Longhaul Duty Hours, it's as close as I can get
