A lot of us Americans are more used to 12 hour clocks then the 24 hour digital LCD clock in K bike instrument cluster.
EASY WAY: If the majority of your riding is done in the afternoon and evening then simply set the clock so that it reads 0:00 at noon. It will then read like a 12 hour clock in the latter half of the day.
HARD WAY: Here's a link to an IBMWR write-up on how to alter the clock's circuitry to function as a real 12 hour clock:
Telling Time The American Way