Inactivity in ArchiOffice/EngineerOffice 20xx disconnects the users after 20 minutes by default and hence they need to re-log in to continue. This is a security setting that cannot be changed within ArchiOffice. However, you can change the timeout settings to any other, say 120 minutes (2 hours), using the following procedure:
On Windows 7/Windows 2008 having IIS 7.0 or 7.5
1. Click the Start menu. In the Search box, type inetmgr and press Enter.
2. Open the IIS Manager. In the Connections panel, select the main connection and choose Session State.
3. Under Cookie Settings, change Time-out to the desired time in minutes, say 120. Click Apply.
4. Now click Application Pools on the left panel and select AO20xxAppPool on the right panel. 
5. Click Advanced Settings and set the Process Model Idle Time-out to 120 (2 hours) and set the Ping Enabled option to False. Click OK.
6. Then go to Default Web Site and click AO20xx>Session State. Modify the Time-out settings as in step 3.
7. When done, click Restart under Actions and re-launch your browser.
Note: If you are still experiencing time-out issue, please check this KB article.
On Windows 2003 having IIS 6.0
1. From the Start menu on your web server, select Run and type 'inetmgr'. Click OK.
2. Expand Local Computer>Web Sites>Default Web Site to show the AO20xx folder.
3. Right-click on the AO20xx folder and select Properties.
4. On the AO20xx Properties dialog, select the ASP.NET tab. Click Edit Configuration.
5. On the ASP.NET Configuration Settings dialog, select the State Management tab.
6. Change the Session Timeout to the desired number (in minutes). Click Apply and then OK.
For more information please refer to:
IIS 7.0: http://technet.microsoft.com/en-us/library/cc771956(WS.10).aspx
Note: If you are still experiencing time-out issue, please check this KB article.