function getmicrotime(){
list($usec, $sec) = explode(" ",microtime());
return ((float)$usec + (float)$sec);
}
 
$time_start = getmicrotime();
 
mysql_query( "" );
 
$time_end = getmicrotime();
$time = $time_end - $time_start;
 
echo "Did nothing in $time seconds";