I posted this in the ZCM forum and Craig thought I might do better over here...I've modified the original post some in light of some of the questions he asked.

ZCM 10.1.3, Win XP Pro, no domain controller, using DLU on the workstations and delivering group policies (including where to find an internet time service) through ZCM.

I have a handful of client machines that are off by about 15 minutes on their computer time but only when regular (Non OES Admin) users are logged in. When I log in (As a member of OES Admins) the time is correct .
Almost all of the users with the time issues are local admins.

I've gone over the group policy that points the machines to an external NTP server and allow all users to make time changes..
On the ZCM side I've cleared cache, unreg, rereg the machines can't think of anything else to do to fix the issue.
I'd like to look at configuring the SP5 client to point the machine to the right NTP server on login rather than waiting for the GP to work.

Any ideas out there? I still have a flat forehead from bouncing my head off the desk.