Hi Bruce,
I did search and also found several links. However this only worked for me when I used it in .items, but never when I defined a var in .rules
Seems I do something wrong 
https://community.openhab.org/t/time-and-date-formatting-in-openhab/70891
https://docs.oracle.com/javase/7/docs/api/java/util/Formatter.html