The code below will print "Event @ $sec" if the time is either :00 or :01. I don't know how taxing it is on the computer. I think that sleep does an alarm + pause call so it shouldn't be spin waiting. The reason for the sleep(30); is so that there is an additional time to correct for error due to sleep(.).

while(1)
{
    ($sec,$min,$hour,$mday,$mon,$year,$wday,$yday,$isdst) = localtime(
+);
    if($sec > 1)
    {
        sleep(60-$sec);
    }
    else
    {
        print "Event @ $sec\n";
        sleep(30);
    }
    
}
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