How do I start an animation for a certain time?

I have the main loop of the program looped using requestAnimationFrame As for example after the character crashed, disable the collision for him for 3 seconds and blink at the same speed? At the same time, the entire gameplay will continue to animate at a different speed

How can I run another animation at a different speed and for a time during one animation?

The code I think is not required here, a standard animation loop using requestAnimationFrame:

function loop() {
    requestAnimationFrame(loop)

    let now = new Date().getTime(),
        dt = now - (time || now)

    time = now

    game.step(dt)
    game.render()
}

thanks