Prefix any of the month tokens with the letter "s" (s for start), to have these tokens appear only on the first day of the month.
On other days the token converts to a blank. Note that this is not a zap token; blank means no text. For example, for an English token:
•On Thursday June 1st, [sm] = 1, [sMMM] = JUN, [sMmmm] = June.
•On May 3rd, [sm], [sMmm], [smmmm] are all blank.