Their isn't a setting in group policy itself to do this, but there is a registry key for it:
HKLM\Software\Microsoft\Wi
ndows NT\CurrentVersion\Winlogon
\ScreenSav
erGracePer
iod : REG_SZ
You could push out the registry key itself with Group Policy Preferences though.
You may need to play around with it to get it working in your environment, some say it needs to be a DWORD others say REG_SZ, some say HKLM work s others say HKCU. I included articles from Microsoft and some discusssions links on it below as well.
http://support.microsoft.com/kb/221784http://social.technet.microsoft.com/Forums/en-US/w7itproui/thread/37ee5887-8b18-4514-b0f5-e81e60b6ccf4