If you want to avoid too much choice, but still want the "the past is immutable" feel, you can prevent editing after noon next day or similar.
Having the default "midnight" be something like 3AM would get you 90% there without any UI changes
I just use a .org file, with git to retain old versions if I edit something that might be of later relevance.
Days "roll-over" when you sleep, so it should be safe to rollover notes which haven't been edited for 6 hours. That way there is no fixed rollover time.