[yangl1996]

A system like Bitcoin has this functionality. "Time" is essentially represented as "depth" of a block, and a block can only be buried deep into the chain with sufficient time (due to the nature of proof-of-work). A cryptographic primitive called "verifiable delay function" provides a good abstraction for this problem.

Specifically, you may put the hash of your message into a bitcoin transaction, and submit this transaction. If you later want to prove its age, just point to the bitcoin block containing your transaction. The guy verifying it is sure that you have got this message before the block is mined, because otherwise you would not have the hash of the message at that time and successfully embed it into a block.