The booth timer allows interpreters in the same booth to keep track of time and the duration of shift. see more information here http://interstaricp.com/forums/topic/booth-timer/
The time is synchronized for all interpreters in the booth automatically.
Best practice: agree before the event who is going to reset the timer after each shift. it will make more sense for the interpreter who is starting the shift to do it. If one of the interpreters forgot to reset the timer you can always reset the timer yourself and it will be synchronized automatically for everyone in the booth.