This is one of the coolest tech things I've seen in a while. Can you explain how the "Check a document" works? I'm not sure I understand how you would check if the timing aligns based only on the text content.
It's a very poorly written way of saying that instead of storing your text it uses a hash of your text to sign. When you want to check the signature you only need to hash the text to check, again without touching the server.