From the Luzern City Guide 2008:

Musegg Wall: A part of the old rampart walls built in 1386. Wall almost entirely intact. Three towers are open to the public: Schirmer, Zyt, and Maennli. The oldest city clock built by Hans Luter in 1535 is on the Zyt tower. This clock is privileged to chime every hour one minute before all the other clocks. (Closed All Saints Day to Good Friday)