How to validate the Chainlink price feed at a specific time

Question

Suppose that in my solidity contract, I need to see the price of ETH in terms of USD at a specific time, say on January 1, 2021. I would like to use the Historical Price Data Feed from chainlink (URL below). I imagine that to achieve this, I would have to pass the roundId as a parameter when calling the outermost function, so that the contract can verify that this roundId indeed gives the price corresponding to the timestamp of January 1, 2021. I am happy with this construction. However, I do not entirely understand the data given back. How do I verify that the roundId indeed corresponds to the timestamp of interest?

URL to the documentation: https://docs.chain.link/docs/historical-price-data/

Interface:

function latestRoundData() external view 
    returns (
        uint80 roundId, 
        int256 answer, 
        uint256 startedAt, 
        uint256 updatedAt, 
        uint80 answeredInRound
    )

Chainlink explanation with these return arguments:

• roundId: The round ID.
• answer: The price.
• startedAt: Timestamp of when the round started.
• updatedAt: Timestamp of when the round was updated.
• answeredInRound: The round ID of the round in which the answer was computed.

Answer 1

The startedAt and updatedAt values returned will give the time (unix epoch) that the round was started and submitted. You can compare this to your 'Jan 1 2021' value