Windows 7: Disable Lock Workstation After 10 Minutes Using Group Policy

To disable Lock:

Under HKEY_LOCAL_MACHINE\SOFTWARE \Microsoft\Windows\CurrentVersion\Policies\System, create a new DWORD value named DisableLockWorkstation and set value to 1.

Then restart the computer.

The answer to the actual question you asked:

User Configuration\Policies\Administrative Templates\Control Panel\Personalization. The required settings are: 'Enable screen saver', 'Screen saver timeout', 'Force specific screen saver' (this is important because if the system has no screensaver configured this won't work) and finally 'Password protect the screensaver'.

from https://social.technet.microsoft.com/Forums/windowsserver/en-US/5c2518d4-f531-471a-a649-0f5dd5495679/group-policy-to-auto-lock-the-system-after-fix-interval?forum=winserverGP