GS-Alpha
My understanding of a duty hour as it applies to Mixed Fleet is any hour from check in to check out, this includes those asleep downroute.
Hence BA's estimation of renumeration is based on 2500 duty hours at 2.40 per hour.
If these 2500 duty hours were solely spent 'at work' I would imagine most crews would hit their 900 flying hours per year legal limit fairly quickly!