Session Timeout Limit in ASP.NET?

The Timeout property cannot be set to a value greater than 525,600 minutes (1 year). The default value is 20 minutes.

Disadvantage: You will have performance issues if you have large number of users and with increase in session timeout, your inactive sessions will remain in Web server memory which may cause application pool to recycle, which would result in loosing all sessions for all users.

by default the value is 20 and the maximum value is 525600 (525600 minutes equivalent to one year). Maintain below code in your Web.config file to maintain maximum session timeout:

<system.web>
    <sessionState mode="InProc" timeout="525600"></sessionState>
    ...
</system.web>

Above one worked for me. Please refer here