code: private static function setETA($done, $total)
      {
          if ($done > $total || $done == 0) {
              self::$_progressEta = null;
              self::$_progressEtaLastUpdate = time();
              return;
          }
  
          if ($done < $total && (time() - self::$_progressEtaLastUpdate > 1 && $done > self::$_progressEtaLastDone)) {
              $rate = (time() - (self::$_progressEtaLastUpdate ?: self::$_progressStart)) / ($done - self::$_progressEtaLastDone);
              self::$_progressEta = $rate * ($total - $done);
              self::$_progressEtaLastUpdate = time();
              self::$_progressEtaLastDone = $done;
          }
      }
docs: Calculate $_progressEta, $_progressEtaLastUpdate and $_progressEtaLastDone
  @param int $done the number of items that are completed.
  @param int $total the total value of items that are to be done.
  @see updateProgress
  @since 2.0.14