Cookies can have something called a “sliding expiration”, which means it will automatically extend the expiration date when you visit. There is also an absolute expiration, so at some point it’ll have to be reset no matter what.

Most likely if you don’t visit for a week, you will get logged out. But if you do visit before it expericed, it just resets the cookie for another week.

I’m not on kbin so I cannot check, but that’s my guess.