I believe you could do this by changing the local accounts logon hours then setting a local GP to force logout when they expire.
net user [user] /times:m-f,08:00-17:00
net user [user] /times:m-f,08:00-17:00
My command allows [user] logons Monday to Friday from 08:00 – 17:00 local time.
Then go into gpedit.msc and set the policy linked below: http://technet.microsoft.com/en-us/library/jj852195.aspx
*Note it won't shutdown the PC it'll log user out, you could find a LGP for that as well maybe.