After you finish diesel, you hang up the pump. The screen then advances to the DEF and says start pumping def--or press def start, something like that. I remove the handle from the def, press the start, and lay it on the ground. Then I move the coach forward to get to the def, and then return and finish filling the def tank.
It may not be necessary to press start in such a hurry, but I have worried about time outs. Most trucks have the 2 tanks next to each other and do not need such a long delay, so it seems reasonable that a timeout would exist.