During all the Varsity games I've done, the only time I ever hit the horn during TOs was to sound 1st horn/2nd horn as the required intervals.
The timing device I normally use is my watch's stopwatch function.
This year am thinking if using my iPod Touch's stopwatch function instead.
The one time I used the time-out timer on the scoreboard controls, the system froze up
Until WIAA instituted the 35 sec. shot clock for boys, I was using the shot clock as the time out timer during boys' games.