Be very careful with this. At my last job we often worked the counter selling tickets/Merchandise, CASA made a point of this counting towards our duty hours, we didn't fly, we didn't go near an aircraft but it was the same company so it counted and whilst they could not enforce hours worked outside in a complete seperate job they were quick to point out, as others here have, that if you turn up to work fatigued because of it and have an accident you're going to be in the pooper!!