You cannot change the Time and Date settings on the IP phones. There is no option to change it directly on the phone.
Changes to the Time and Date on the phone should be made through the Cisco CallManager because the Cisco CallManager is the server in charge of sending the time to all the IP phones. Also, the time and date changes made in the Cisco CallManager are be clusterwide, but not on any particular IP phone.
To change the time and date displayed on the IP phones, perform these steps:
Go to the Cisco CallManager Admin page, and select System > Date/Time Group.
Set the date and time according to your requirement.
Reset all the devices, or restart Cisco CallManager service during off production.
For related information about configuring Cisco CallManager for date and time, refer to these documents: