Well, it wasn't as such an argument as a disagreement. I stopped immediately as I could see it going nowhere. But it got me wondering. If the task had been "row for 40 seconds" then it would be clear - but then, how far did you row in 40 seconds? I would say that you rowed the distance the monitor says at 40 seconds but actually the machine glides farther afterwards - should that be counted in?
I personally think we both are right. If it were a race, it would be stupid to stop rowing before reaching the goal as you reach it faster by rowing but if it's just for getting over the finish line, then sure, stop rowing. As we were doing it for the exercise, I find it a bit stupid to stop as you lose out on the last three pull-backs.