"Changed group membership in WGM 10.6.3 from the 10.6 server. The change takes overnight to work"
If I've understood you correctly I've never known this or anything else to take that long? What were you trying to do exactly?
"Formerly ran WGM from my 10.6.8 mac (worked perfectly) but now I am at 10.7.5 and must use WGM on the server. Has anyone else seen this behaviour?"
What were you trying to do exactly?
From my imac (10.7) I sign in to remote server (10.6.8) using server admin 10.7. Select screen sharing, launch WGM. Select one user from a group. Delete user and save. I tested this deleting myself (user abc not admin) from group. Disconnect from server as user abc on my imac. Re-connect to server as user abc. Still have all permissions to share points that should not be so if removal from group worked. Restart imac ... user abc still has all permissions an hour later. Eventually it will take, typically I find it working the next morning at work. I am asking because this is not the first time I have seen this. When my imac was at 10.6.8 a month ago and I used WGM from my imac deleting a user from a group worked instantly for years. Not so now.
Thanks for your interest.
I've never seen the problem you describe, then again I don't use Server Admin in the same way.
Although it should work using Server Admin I would not connect to the Server in that way. Have you tried to simply VNC to the Server itself launching WGM and making the change? It should work immediately, leastways it does for me every time.
IMO I would not use a newer version of the Server Administration tools on an older server even though the Support Article says you can. In my experience doing this can cause random and unexpected results.