This timekeeper comprises a first timer ( 4 ), means ( 12 ) for connecting it selectively to the train of the timekeeper (T), a second timer ( 5 ), a synchronous coupling between the first ( 4 ) and second ( 5 ) timers, and fly-back means ( 13, 13', 9, 11 ) for said timers ( 4, 5 ). An auxiliary motive source ( 10' ) is in a driving relationship with the second timer ( 5 ) and a one-way coupling ( 6 a , 7 a) is situated between the first ( 4 ) and second ( 5 ) timers to regulate the speed of movement of the latter at a predetermined ratio with the speed of movement of the first timer ( 4 ) while allowing one-way relative movement of the first timer ( 4 ) relative to the second ( 5 ) when the latter is in the stop position and one-way relative movement in the opposite sense of the second timer ( 5 ) when the first timer ( 4 ) is in the stop position.