The phrase “marking time” is a military command for soldiers in close-order drill to stop their forward progress but to keep their feet moving in precision so they can quickly resume marching on command.
Marking time means that although your progress has been temporarily stopped you are fully prepared to continue when the time is right.
On the other hand, “killing time” means that you’re doing absolutely nothing.
Or as the proverb says, “You don’t kill time, time kills you.”
