If you’re already signed in and simply want to sign in as a different user, you can go to the /login.html page of your page and sign in as a different user. The moment you sign in with a new user, your old XASSESSIONID with disappear and a new session is generated.
As for the session timeout value, this is 10 minutes by default. You can check this here:
I hope this answers your question :)
I believe the default is 5~15minutes. And indeed when you logout one user, you'll be able to login with another user.