prevent access to webpage by date and time

Do you know any php?

You could do something like below, hard code the date at which point onwards you want the link to appear:

<?php
$date = date("Y-m-d");
if($date >= "2021-03-15") { ?>
<a href="showInfo.php?showInfo="true">Link</a>
<?php } ?>

On the showInfo.php page which the link is set to go to check to see if the 'showInfo' url parameter is set:

<?php if(isset($_GET['showInfo'])) { ?>
<h1>Welcome</h1>
<?php } else { ?>
<h1>No Access</h1>
<?php } ?>

does the code scare you, or can you write a few lines... this link should help you... in fact the HTML content will only be visible according to date ranges

https://stackoverflow.com/questions/4319135/jquery-or-javascript-that-display-content-based-on-the-date-help

Don't publish the page until that certain date and time.