CI 4.3.5 - Session Expiration Not Working

I don't understand what is your exact issue? "does not work" explains nothing.
It is better to show what you want and what was happened.

7200 means the lifetime of the session cookie. You can see the value in your browser's developer tool.
If the time has passed (in the browser's clock), the browser deletes the cookie, so the user must re-login.
But if the session data in your server is deleted, the user must re-login when the session cookie still exists

That what i means to say

After setting

Code:

public int $expiration = 7200; // 2 hour

Even after setting above, the browser is not deleting the session / cookie, so the user re-login. Users are still login only, i to tested - waited almost 4 hours and still Login only.

I have to delete session data from writable >> session folder manually so that users must re login. but that is not solution , its should work with

Code:

public int $expiration = 7200; // 2 hour