If you're talking about the delay from the time you enter your credentials and hit enter to when a desktop shows up, have you tried enabling verbose login message so you can see if it's a group policy problem, file redirection, etc?
There are two Group Policy setting you have to change to see the detailed login messages:
Computer Config/Policies/Administrative Templates/System/Verbose vs normal status messages - this one needs to be enabled
Computer Config/Policies/Administrative Templates/System/ Remove Boot/Shutdown/Logon/Logoff status messages - this one needs to be disabled
Once you have that GP in place you may be able to see what's causing the slow login instead of just watching the "welcome" message.
Geoff