Tests if a string is a valid time for a 24hr clock.

is_valid_time.js

function is_valid_time(value) {
	/* Validates that a string is a valid time in either of the following
	 * formats:
	 * 
	 * HH:MM
	 * HH:MM:SS
	 */
	regex = /^([01]\d|2[0-3])(:[0-5]\d){1,2}$/;
	return regex.test(value);
}