A hash of what exactly though? This would only work as a timestamp, if you ever plan to publicly release your secret. But it wouldn't work if you e.g. want to

A hash of what exactly though? This would only work as a timestamp, if you ever plan to publicly release your secret. But it wouldn't work if you e.g. want to find other people that also know what you know, without ever telling anyone. (Because they wouldn't have your exact text or document to hash...)