This seems to get searched quite alot so here is a quick explanation:
You cannot change the time using the KX-T7667 handset. This handset is the basic model and does not have the ability to enter program mode (which is a requirement for changing the time)
All other Panasonic handsets ( KX-T7630 & KX-DT333 ) are able to change the time.
It is quite common to find offices where all phones are the smaller KX-T7667 model. Clearly this is an oversite by the phone system company as it makes changing basic system settings impossible.