Identical to mktime() except the passed parameters represents a GMT date. gmmktime() internally uses mktime() so only times valid in derived local time can be used.
Like mktime(), arguments may be left out in order from right to left, with any omitted arguments being set to the current corresponding GMT value.
hourThe hour
minuteThe minute
secondThe second
monthThe month
dayThe day
yearThe year
is_dst
Parameters always represent a GMT date so is_dst
doesn't influence the result.