__pmMktime man page
__pmMktime — convert a tm structure to a calendar time
time_t __pmMktime(struct tm *timeptr);
cc ... -lpcp
__pmMktime is very similar to mktime(3), except the timezone used is the current “reporting timezone” (rather than the default TZ environment variable scheme).
Like mktime(3) the time to be converted is passed via timeptr, and the function result contains the calendar time (the number of seconds since 00:00:00 UTC, January 1, 1970).
The default current reporting timezone is as defined by the TZ environment variable, so __pmMktime and mktime(3) will initially produce similar conversions.
Use pmNewZone(3), pmNewContextZone(3) or pmUseZone(3) to establish a new current reporting timezone that will effect __pmMktime but not mktime(3).
mktime(3), PMAPI(3), pmCtime(3), pmLocaltime(3), pmNewContextZone(3), pmNewZone(3) and pmUseZone(3).