Ron Rosenfeld wrote:
Dunno about Piper, but I got a replacement digital clock for the yoke mount
in my 1965 M20E to replace the 7-day windup analog original.\

Almost certainly an 8-day windup. That was standard for the genre. The
idea was you picked a set weekly schedule to wind it (i.e. every Monday
morning), and it never got down below 1 day's worth of winding left.