if (new Date().getHours() > 20) {
document.getElementById("carttext").remove();
}

<div class="block block-cart-header" style="padding: 0px;" id="carttext">
    <div class="block-content" style="background: none; padding: 2px; min-height: 10px; text-align: center; background-color: #e2e2e2;">
        <span style="font-size: 10px;" id="ordertext">Modtag <span id="day1"></span>, bestil før</span><br>
        <b id="countdown1" style="color: black;"></b>
    </div>
</div>