Like most things in Scouting, it depends what you want to make of it. It can include things like stepping into a section to lend a hand, running a meeting because a leader is ill and there is nobody to cover, setting up or helping at badge/skills courses - the list is endless. When I've done it in the past, it's actually been quite a relaxed role and not terribly time consuming BUT that is no guarantee of course. I would suggest that you go back to whoever asked you and ask how they see the role and why they think there is a need for a DSL. But before that, decide how much time you want to offer - then apply the Scouting factor and remember that someone once told you "It's only a couple of hours a week".