This will create a new ball three times, one every 2 seconds. To create more simply change the 3 in the for loop and more will be created, 1 every 2 seconds.
function CreateBall(){
ball = {
x : canvas.width,
y : Math.random()*canvas.height,
speedX : -130,
speedY : 0,
radius : 10,
color : "red",
};
}
for (i=0;i<3;i++) setTimeout(CreateBall, i*2000);