I've been on the Flight Deck, and on approaching the Holding Point, have heard XXX123 are you ready Immediate?. If yes, then a/c is cleared for an "Immediate Take Off". A/c "spools up the engines" [advances the throttles] and enters the Runway...and departs.
IF not ready, then hold until they are.
Also in 35 years of [Civil] Aviation, I've lost count of the number of "rushed" departures
watp,iktch