code: public function getFirstTimestamp($tags)
      {
          // extract the TimePoint identification from the provided item, and find existing range
          $range = $this->getRange($tags);
          $last = false;
  
          if (count($range)) {
              $last = $range[0]->getTimestamp();
          }
  
          return $last;
      }
docs: Gets the first timestamp of the range for the provided tags
  @param string|array $tags
  @return float $timestamp