I discovered that the time on our AD/DC is out of sync (or faster by about 5-6 minutes)...obviously this caused the time on all our client machines to be faster too.
I would like to know can I adjust to the correct time via the clock on the taskbar on my AD/DC..?
if so, which AD/DC should I change..and how to change ,how to take immediate effected for all client
If you aren't configuring an external time source, then -- yes, you should be able to modify the time on the PDC Emulator. But, five to six minutes is a HUGE time gap which will absolutely cause trouble if you modify it all at once. How time sensitive is your network? Can you make 15 to 30 second changes on the PDC Emulator every night before you leave for the day? In any event, I wouldn't try to make changes larger than 120 seconds at a go. Once you make the (small) change on the PDC Emulator, the other systems in the network will attempt to slowly bring themselves into sync.