const maxTime = 1 * 60 * 1000;

​

let freq = (maxTime - 1000) * 0.1;

let countTime = 0;

let prevTime = 0;

​

function setup() {

  createCanvas(400, 400);

  print(freq)

}

​

function draw() {

  let curTime = millis()

  countTime += curTime-prevTime;

  prevTime = curTime;

  if(countTime < freq/2){

    background(255);

  } else{

    background(0);

  }

  if(countTime > freq){

    freq = (maxTime - curTime) * 0.1;

    countTime = curTime%freq

    print(freq)

  }

}