When a call is made or answered on a call appearance, the call appearance line can include a call timer. This is controlled by the phone's Call Timer setting.
During the call you may want to show or hide the call timer associated with the currently selected call appearance; for example, in order to see more of the caller ID information. Temporarily turning the call timer of the currently selected call appearance on or off can be done using a Timer button.
Note that when the call appearance is next used, the Call Timer setting determines whether or not the timer is initially displayed.