$lastGood = time();
while( 1==1) 	
{
	#print ".";
	#print time(), "\t", $lastGood, "\n";
	if ((time() - $lastGood) > 300)		#if it has been 5 minutes since the last check, check again
	{

            #do something
            $lastGood = time();
	}
	
	
}