If you want to set up Central Time (Chicago) on you deice you
ntp server [IP of your NTP 1 server] ntp server [IP of your NTP 2 server] clock timezon UTC -6 clock summer-time DST recurring 2 sun march 02:00 first sun nov 02:00
And now we can verify:
#sh clock det 16:17:47.512 DST Thu Apr 25 2013 Time source is NTP Summer time starts 02:00:00 UTC Sun Mar 10 2013 Summer time ends 02:00:00 DST Sun Nov 3 2013
Look at the US Daylight Saving website to check if you have done it right.