How to made an object appear after a delay in p5.js

I intend to draw dilating circles. First a small circle appears on the center of the screen then radius increases and the circle enlarges, 2 seconds later another circle appears and also enlarges. At the same time there could be multiple concentric circles, looping infinitely.

This is the current code, but I have problems in making the 2nd circle appear 2sec after 1st circle, and 3rd circle 2sec after 2nd circle etc.

let w=500,h=500;
function setup() {
    createCanvas(w, h);

function draw() {
    ellipse(w/2,h/2, r*frameCount/2, r*frameCount/2);
    //2 seconds later, this new circle appear
    ellipse(w/2,h/2, r*frameCount/2, r*frameCount/2);

you need a timer!