1. Go to the Scheduled Tasks tab in your Control Panel
2. Create a new Scheduled Task and select the Steam Update option
3. Give it a name of your choice, 4 Hour Steam Update for example
4. Select the date/hour you want to next restart will to go
5. Select Recur Every 1 Days
6. Select Repeat task option
7. Select Repeat Every 4 hours
8. Select For 24 Hours
9. Select the Script Parameters tab on top and change it to Update only if a new version is available
10. Save the task

Only when new Versions are available.