You would be better to print the message (web site or whatever) when a particular event occurs, like a Race Start, or as the player leaves the pits. Have a look around the code for the events OnRaceStart, OnNewPlayerJoin, and OnConnect.
From a coding perspective however, here's how to do a recursive function:
<?php
CatchEvent OnLapperStart()
DelayedCommand( 120, ShowAnnouncement );
EndCatchEvent
Sub ShowAnnouncement ()
globalMsg( "Visit our website at http://isntthisannoying.com");
DelayedCommand( 120, ShowAnnouncement );
EndSub
?>
That will display the announcement every 2 mins and people will be compelled to visit your website that often, and do this -> :banghead:
PS: You will not be able to stop it.