ts:daylight.savings

Set Daylight Savings Time - Cisco Phones

This may also work on other Cisco models as well, but may be found in a different location.

On the Cisco phone web GUI, under the Regional Tab, scroll to the bottom and in the Time section, place the following text in the Daylight Saving Time Rule box.

Note to U.S.A users. The following example reflects the new change starting March 2007.

DST starts on the second Sunday in March and ends on the first Sunday in November:

start=3/8/7/02:0:0;end=11/1/7/02:0:0;save=1

Just select the correct time zone offset (-6 for Central)
Select Yes for Ignore DHCP time offset, and
Select Yes for DST Enable.
(If you are using the no offset GMT, then select No for DST Enable.)

If you want 24hr display instead of 12hr, change that on the User tab on the right.