Many users like me need to keep track of multiple time zones, there is a nice feature in Windows 7 to help users keep track of time of Multiple Time zones in your system tray. Using this feature you can set up to 3 clocks from 3 different Time Zones at a time.
Well, you can do it in some easy steps :
1. Right click on clock in system tray > Adjust Date/time.
2. Now go to tab Additional Clocks... here you will see two frames.
follow the image for better understanding>>>
3. After Adjusting the time zone, click Apply and OK.
Still in system tray you will see only time of ur main zone, but whenever you need to see time of other Zones, just hover over the time of system tray, you will get something like this pic.