When you have calls alerting on appearance buttons, the phone can include a timer in the appearance details shown on the display.
The timer shows how long the call has been alerting.
When you answer the call, it resets to show how long the call has been connected.
The timer also shows how long a call has been on hold when you hold the call.
You can turn the timer display on or off. Turning it off provides more space for other call details on the display.
To do this during a call, press the PHONE key and then press Features.