Piezo doesn't behave well with setWatch()

@maze1980, my belief is that @barry_b_benson desires to have the display illuminated for the entire duration the button is held down and not just a simple timeout after a button press as your simplicity implies. Yes it is blocking, but what else in this case would want to interrupt? As you suggest, If the LEDs are turned on, then a unique new event (another button press perhaps) will be required to turn them off. I'll defer to his response for confirmation.

Maybe this is what you had in mind??   Untested

var intervalID = {};
function ct() { clearTimeout( intervalID ); }
// Easier to type ct() than entire line

 
var delay = 5000;    // msec  Turn off in case button remains stuck down
var isButtonDown = false;  // Not used here but might be needed elsewhere

function startTimer() {

  isButtonDown = true;
  
  hoursDisplay();    // Turn on as code inside func() occurs after timeout

  intervalID = setTimeout(function () {

    clearDisplay();
  
  }, delay);
}

function stopTimer() {
  isButtonDown = false;
  ct();
  clearDisplay();
}

function clearDisplay() {
  display(1, clear);
  display(2, clear);
}

function hoursDisplay() {
  display(1, hourFirstDigit);
  display(2, hourSecondDigit);
}


setWatch(function(e) {
  stopTimer();
}, select, {repeat: true, debounce: 50, edge: "rising"});