    function getLatestPrice(address _token)
        public
        view
        returns (int256 nowPrice)
    {
        ...
        if(timeStamp == 0)
            revert TimestampZero();
        return price;
    }
+   uint constant observationFrequency = 1 hours;

    function getLatestPrice(address _token)
        public
        view
        returns (int256 nowPrice)
    {
        ...
        (
            uint80 roundID,
            int256 price,
            ,
            uint256 timeStamp,
            uint80 answeredInRound
        ) = priceFeed.latestRoundData();

        uint256 decimals = 10**(18-(priceFeed.decimals()));
        price = price * int256(decimals);

        if(price <= 0)
            revert OraclePriceZero();

        if(answeredInRound < roundID)
            revert RoundIDOutdated();

-       if(timeStamp == 0)
+       if(timeStamp < block.timestamp - uint256(observationFrequency))
            revert TimestampZero();

        return price;
    }
