How to add a special Woocommerce “buy now” button?

If you do not wish to add the product to the cart them simply go into your content-single-product.php file and create an element that has an anchor tag that links directly to your cart wherever you want it to show up.

so it’d be something like:

<div class="cart-redirect">
    <a src="http://yoursite.com/cart">Checkout Now</a>
</div>

and just style it to look like a button.