by default odoo. set 90 days validity for session_id and it's incremental if you ever access odoo within 90 days it will extend its validity from access day/date

you can change validity from here
https://github.com/odoo/odoo/blob/13.0/odoo/http.py#L1400 => 90 days = 90 * 24 * 60 * 60 seconds

It's not a security risk as far as your physical device secure and no one can steal your session_id from your browser 

Note: odoo don't track all the login devices so in case of a stolen physical device you can not log out from that device.

Hi Ravi,   Thanks for your answer.   

We are using the MS Active Directory (AD) password verification and our security concern is because we do not see Odoo to be querying AD every time a user logs in.

How often is the password verified against AD?   

What happens if a session is open in Odoo for many days (because the session is still valid in the cookies) and the user is blocked or deleted from AD?