for loop

Delay is not a good way to manage time dependant tasks as it uses all the resources for itself
You can do it this way:

var maxTime = 500;
var maxStep = 10;
var count = 0;
var timer;
var state = false;
var blinkActive = false;

function blink(){
  state = !state;
  digitalWrite(LED1,state);
  if (!state) count--;
  if (count===0){
    clearInterval(timer);
    blinkActive = false;
  }
}

function launchBlink(){
  if(blinkActive === false){
    count = maxStep;
    timer = setInterval(blink,maxTime);
    blinkActive = true;
  }
}

function onInit(){
  clearInterval();
  LED1.write(0);
  setWatch(launchBlink,BTN,{repeat: true, edge: 'rising', debounce: 100});
}

onInit();