How Do I Force My Computer Users To Log Off After 30 Mins?

You can take advantage of the Windows Task Scheduler
Here’s How:
Using Task Scheduler to schedule the computer to shut down and restart at a specific time
* Click Start, Run and type control schedtasks
* Double-click Add Scheduled Task. The Scheduled Task Wizard starts.
* Click Next.
* Under Click the program you want Windows to run, click Browse.
* In the Select Program to Schedule dialog box, locate the %SystemRoot%System32 folder, locate and click the Shutdown.exe file, and then click Open.
* Under Perform this task, specify a name for the task and how frequently you want this task to run, and then click Next.
* Under Select the time and day you want this task to start, specify a start time and date for the task, and then click Next.
* Type the user name and password to run this task under, and then click Next.
* Click to select the Open advanced properties for this task when I click Finish check box, and then click Finish.
* Click the Task tab. In the Run box, specify any additional parameters that you want to use with Shutdown.exe. Click OK.
Important: In the 10th step, you need to add the parameters for the Shutdown.exe command. To immediately shutdown the system (0 second timeout), the command-line would be:
shutdown.exe -s -t 00
To reboot the system immediately, this command:
shutdown.exe -r -t 00
For additional help, type Shutdown /? at the Command Prompt. Scheduling the Shutdown.exe without any parameters will not help. It will just execute with a exit code 0 (success)