code: public function toDateInterval(float $duration) : DateInterval
      {
          Preconditions::checkState($this->dateIntervalFormat !== null, '[%s] does not support toDateInterval()', $this);
          return new DateInterval(sprintf($this->dateIntervalFormat, $duration));
      }
docs: Creates a DateInterval with the given duration and this unit.
  
  @param $duration float
  @throws \Exception if this object does not have proper DateInterval format string
  @return DateInterval