1. Run the command gpedit.msc. You will need to be an elevated user to manipulate Local Group Policy Editor.
2. Navigate to Local Computer Policy > Computer Configuration > Administrative Templates > Windows Components > Windows Update.
3. Look at Configure Automatic Updates, it should be set to "Not Configured". In order to set up specific date and time for the Windows updates to occur, change it to Enabled and set up date and time.
The following is a screen shot of what a server would look if it is to be rebooted every Sunday @ 00:00 hours.