I really can't see such a wait is justified. When the runways switch over at 3pm, the first departure in the queue is cleared from the holding point the moment the last arrival touches down, and is given the go the moment it clears. It's "Gatwick style". Get the departure on the other runway to line up at the same moment, off you go. There might be a slight loss of efficiency on the departure runway (compensated by shooting off two together), but maybe just one loss of landing, if that. What do our ATC team say ?