I think there's an advanced setting for this in the App Pool.

Have a look at the following two KB's

Browser disconnects users when they are inactive.

 Sage 300 Web Screens Adjust idle time logout session.

Just as the others said, its under the Process Model subheading under the Advanced Settings for the Sage 300 App Pool - Idle Time-out (minutes).

it is important that you are changing the setting in the <program files>\online\web directory    there are a lot of postings saying to change this setting that exists in other web config file but non of them work except the one in the program directory.  Thank you for the help.

changing the settings noted in this thread does control the length of time out however what I am finding now is that if they lock their workstation and unlock it - no matter how long the time out setting is at it requires them to login again.  Does anyone have a solution for that?

Assuming this isn't the AppPool recycling (yet another setting different to the ones above), the problem is likely the network card or machine sleeping while its locked.  All I can think of is ensure your users are on Maximum performance power profiles with the computer, display, wifi, network, hard drive  and literally anything else set not to sleep.  Especially on modern PC's with aggresive power saving - even at the motherboard level, the temptation of an important component going to sleep while locked breaking your Sage session will be huge - I think this is going to be a tough battle but if you solve it let us know!  Maybe your users can change to a screensaver with lock on wake instead of just locking their PC with the screen going blank?