I'm not sure what the value proposition is here. Is the idea that you want to use this later to tell others you had the idea first, or to protect your IP?
If so, I could definitely see people noting every conceivable idea they can imagine to claim rights later
... Otherwise, is it because I don't trust my past self to be accurate?
Or to prove to 3rd parties you absolutely did what you said you did at a time? In which case it's not private.