JSFiddle - React, Tailwind, and code Playground

HTML

<img id="bgqueue" />

CSS

html, body {
    height : 100%;
    width : 100%;
}
body {
    background : url('http://baltimorepostexaminer.com/wp-content/uploads/2012/07/spider-man2_pole_4681.jpg');
}
#bgqueue {
    display : none;
}

JavaScript

setTimeout(function () {
    $('#bgqueue').attr('src', 'http://upload.wikimedia.org/wikipedia/en/thumb/1/1d/Thor_God_of_Thunder.jpg/256px-Thor_God_of_Thunder.jpg').on('load', function () {
        $('body').css({
            'background-image': 'url(' + $(this).attr('src') + ')'
        });
    });
}, 3000);