In this mission the bridge can be destroyed as soon as the "flat bed" truck starts moving. You can see this vehicle on the map and so the goal is to hit the trigger to make it move as soon as possible and then blow up the bridge. Also at the start I do a grenade boost that saves 1 second. We don't swim any faster or slower with any item in the players hand so i figured I would add a grenade boost to save a second.