The Collaborative International Dictionary
three-minute glass
Hourglass \Hour"glass`\, n. An instrument for measuring time, especially the interval of an hour. It consists of a glass vessel having two compartments, from the uppermost of which a quantity of sand, water, or mercury occupies an hour in running through a small aperture unto the lower.
Note: A similar instrument measuring any other interval of time takes its name from the interval measured; as, a half-hour glass, a half-minute glass. A three-minute glass is sometimes called an egg-glass, from being used to time the boiling of eggs.
Usage examples of "three-minute glass".
The Master would ask, and if the riddle was still unanswered after the sands in a three-minute glass had run out, that contestant had to leave the line.