Correct. The protocol itself allows the note creator to specify the timestamp.
It’s possible to narrow the creation date considerably by including information from and encoding information back into the Bitcoin blockchain.
Discussion
I see - including the hash of the latest block in the post tells you it can't have been written before today (which comes for "free"), however to prove it couldn't have been written *after* today, you'd have to write something like the note id + hash into a bitcoin OP_RETURN
Exactly. Although a single OP_RETURN can prove any number of stamps using a Merkle tree. I believe this is what open timestamps does.