How to replace text which is not in the DOM while page loads

I am not an expert in javascript or jQuery. I want to replace a text that is not in the DOM while the page loads. After clicking a button the text appears. This is the code I am using....

$(window).load(function(){
    $(document).on('change', '.shippingquote', function() {
        $(this).html($(this).html().replace(/Free Shipping/g,'Free Shipping (4-8 days)'));
    });
});