Not at all, for several reasons...
the best route to go down would be
PHP:
<?php
$page1 = 'pages/after315.html';
$page2 = 'pages/before315.html';
if ((date('G') > 15) || ((date('G') == 15) && (date('i') >= 15)))
require_once($page1);
else
require_once($page2);
?>
Simply put, that checks if the current server hour is after 15 (3pm), or if it is 15 AND the minutes have reached 15.
After that it will use the require() function to load a different page. Should it be the right time, it will load one page, else it will load a different one. Those pages were defined in variables are the start.
This will use the server time. Every day, page 2 will load from midnight until 15:15, which will then show page1 until midnight