code: public static function secondsBetweenDates($start, $end, $absolute = true, $timezone = 'Europe/Prague')
      {
          $timezoneObj = new \DateTimeZone($timezone);
          $date = new DateTime($end, $timezoneObj);
          $diff = $date->diff(new DateTime($start, $timezoneObj), $absolute);
  
          return ($diff->invert ? -1 : 1) * (($diff->days * 86400) + ($diff->h * 3600) + ($diff->i * 60) + $diff->s);
      }
docs: Get difference between two dates in seconds
  
  @param string $start Start date in DateTime compatible syntax
  @param string $end End date in DateTime compatible syntax
  @param bool $absolute Return absolute (positive) number
  @param string $timezone Timezone @see http://php.net/manual/en/timezones.php
  @return int Difference in seconds