_extractLastTimestamp(value) {
      if (!value || !this._checkValueValidity(value)) {
        return undefined;
      }
      const dateStrings = this._splitValueByDelimiter(value);
      if (dateStrings[1]) {
        const parsedDate = this.getFormat().parse(dateStrings[1], true);
        return parsedDate.getTime() / 1000;
      }
      return undefined;
    }
Returns a UTC timestamp, representing the last date in the value string or undefined if the value is empty or there is just one date
@private