Excellent question -- there doesn't appear to be a 'format parameter' for AM/PM in the CMOD 8.5 online help.
The conventions in the online documentation are extremely similar to UNIX date formatting, so you may be able to use them.
https://en.wikipedia.org/wiki/Date_%28Unix%29Specifically:
%l (Percent-Lowercase-L) for 12-hour clock hour field.
%I (Percent-Captial-I) for a 12-hour clock with a leading zero.
%p (Percent-Lowercase-P) for uppercase AM/PM
%P (Percent-Capital-P) for lowercase am/pm.
(These two seem backwards, no?)
On my system, %p gives 'pm', and %P gives 'P' -- which could either be single-character PM, or maybe it doesn't recognize that code and simply prints the letter P.
Give it a try and let us know how it turns out.
-JD.