From GridLAB-D Wiki
dateformat - Determine the format of timestamp strings
Synopsis
gridlabd --define dateformat=ISO
#set dateformat=ISO
ISO
The date/time format is yyyy-mm-dd HH:MM:SS ZZZ.
US
The date/time format is mm-dd-yyyy HH:MM:SS ZZZ.
EURO
The date/time format is dd-mm-yyyy HH:MM:SS ZZZ.