Please wait for User Profile Service... on WIndows 7 takes around 1-2 minutes to process

Have you looked for Event Log errors during the time of logon on these workstations? Also, I'd recommend turning on Verbose messages via GPO for some workstations you can troubleshoot on to see where it is taking the longest.

In a Computer GPO: Administrative Templates\System\Display highly detailed status messages - enable. Run GPUPDATE /force and reboot. Now when you logon you'll get more descriptive messages to help in troubleshooting where the delay is.

We have got the “waiting for the user profile service” problem solved.

For our case, we are not using roaming user profile but we have found that our AD users have specified Home Drive in network drive. So we just changed the AD user home drive to “Local” (with no drive specified)

To validate where is your home drive and home path is just execute SET command in CMD and browse for HOMEDRIVE and HOMEPATH. For our case, we want to ensure that it's D:\ and \Users\xxxx

Good Luck. I am Number 9