How to visually time your web chat or voip session

Can someone point me in the right direction? I want some sort of a button that visually shows me and the other person how long our web chat or our voip conversation has been going. I want this timer button to allow me or the other person to stop and start the timer at our discretion as we chat/talk. Is there anywhere I can find such a plugin/button?

I wasn’t sure where to post this, if i’m in the wrong section? can you moved the thread to that section?