One thing that I think is fun to do as a DM, and adds a bit more urgency to urgent in-game moments is to slap an hourglass down on the table. (A la Matt Mercer, that man has given me more ideas than I can count) Whether the room the PCs are in is filling with water, or the walls are closing in and they need to find a way to stop it, or maybe just if they are in a rapidly burning building, giving them a visible time limit is something that I think adds a bit more urgency and fun to the situation. I'd love to see that in some way implemented into Roll20 so I can portray time-sensitive encounters in a more engrossing way.