Hi there,
it is possible with Javascript.
Add this JS to the wp_footer
hook:
<script>
window.onload = function() {
document.getElementById('fade-in-button').className = 'active';
};
</script>
And add this CSS to the site:
#fade-in-button {
opacity: 0;
transition: opacity 0.2s ease-in;
transition-delay: opacity 5s;
}
#fade-in-button.active {
opacity: 1;
}
Then give your button an ID of fade-in-button
The only problem is if a user has JS disabled in their browser the button may never appear.
There is ways around that but it would involve the button being visible to begin with.