Password protecting pages — how does it work??

I can’t quite figure out what’s happening with the built-in password protection on a single page. When I activate it, it works fine. But then every time I visit that page, I’m granted access without having to re-enter my password. That’s fine, but when does that page get re-protected? I’ve restarted my browser and I’m still granted access. I’ve cleared my cache and cookies and I’m still granted access. When does that get re-set so the user would have to re-enter the password?

What are the parameters for password-protected access? I can’t figure this out! Thanks…