Can you do by just subtracting 144 from the block height per day you're looking?

If not, I'd still recommend doing that and then looking up the api for a block explorer (like blockchain.com) and trying to programmatically go back (or forward) from there based on how many blocks would have come since. I remember blockchain.com's api indexing blocks based on height and hash (not sure how others do it but it's probably an easy enough place to start and get a json of data, and then checking the time the block was received or generated).