One way to motivate players to get a move on and stop dawdling is to enforce in-game time pressure. The ticking time-bomb, the dragon bearing down on them, or the cunningly constructed supervillain deathtrap. Often players have time to discuss strategies and come up with plans, even when in-game they really shouldn't have that much time.

But there are cases when it can be good to remind the players that they really don't have enough time to do anything but whatever they come up with in a brief moment of panic.

Some suggestions for achieving this: Use an egg timer, with various amounts of the sand already in the bottom bulb. Or a digital countdown timer (especially good for time bombs). You need to make sure the players can see the time ticking away - a surprise alarm is no good. Unless you're being really devious.

Transcript

R2-D2: Don't forget you have Force Pull.
Luke: I'm just a fighter pilot, not some sort of mystical hero with magic powers.
C-3PO: There's nothing magical or mystical about midi-chlorians.
Luke: But I don't feel anything.
R2-D2: That'll be the frostbite spreading.
GM: The wampa sees you stirring, drops the bloody bone it was chewing, and stands up.
Luke: I suppose it's too late to disguise myself as an icicle.
GM: The wampa approaches.
Luke: Damn. I'm not gonna die like this. No way. I... I use the Force.
GM: Roll.
Luke: 10.
GM: The sword leaps into your hand.
[SFX]: Whooom!
Luke: I swipe the ice.
[SFX]: Slice!
[SFX]: Krunch! {Luke falls}
Luke: Can I count my legs without looking at the ceiling?