code: def increment_day_start_ut(self, day_start_ut, n_days=1):
          
          old_tz = self.set_current_process_time_zone()
          day0 = time.localtime(day_start_ut + 43200)  # time of noon
          dayN = time.mktime(day0[:2] +  # YYYY, MM
                             (day0[2] + n_days,) +  # DD
                             (12, 00, 0, 0, 0, -1)) - 43200  # HHMM, etc.  Minus 12 hours.
          set_process_timezone(old_tz)
          return dayN
docs: Increment the GTFS-definition of "day start".
  
          Parameters
          ----------
          day_start_ut : int
              unixtime of the previous start of day.  If this time is between
              12:00 or greater, there *will* be bugs.  To solve this, run the
              input through day_start_ut first.
          n_days: int
              number of days to increment