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You could use the setTimeout() JavaScript method for that:

function delay() {
    id = window.setTimeout(rm, 500);
}
function rm() {
    // Remove the notice from the DOM.
    var e = document.getElementById("id_of_the_notice");
    e.parentElement.removeChild(e);
}

Note:

• 500 (milliseconds) can be changed.
• id_of_the_notice must be changed

You could create a .js file in your child theme which you could use for all of your custom JavaScript. You’d then enqueue it with the following code (which goes into your child theme’s functions.php):

function my_enqueue_scripts() {
    wp_enqueue_script( 'my-custom-js', get_stylesheet_directory() . '/js/script.js', array(), '1.0.0', true );
}
add_action( 'wp_enqueue_scripts', 'my_enqueue_scripts' );

Note:
This snippet will enqueue a script called script.js located at child-theme/js/script.js

Alternatively, you could just add the code to your footer.php file, just above the </body> tag like this:

<script>
    // JavaScript goes here.
</script>

$handle is simply a name you give your script. I chose my-custom-js but feel free to use any string you like. custom-script or maelga-js are both suitable alternatives.