Answer
The period of oscillation for a mass attached to an ideal spring would make for a good measure of time.
Work Step by Step
The force of an ideal spring is conservative (no energy is lost from the system). In ideal circumstances(the mass is sliding across a frictionless surface with no air resistance) the amount of time required for the mass to go from the central point where the spring has no tension to either end of its oscillation and back will never vary.
For this reason it would be an ideal interval to mark as the "tick" of a timepiece.
