Thank you for answering, it is true that if someone has access to the server you might be in trouble, but if he has access to a cpu monitor, he might also have access to RAM and could just get the data from there.

For the precision of sleep, http://php.net/manual/en/function.time-nanosleep.php might be more appropriate

Also, you would only need to slightly clamp very important functions, so DoS attacks aren't that likely on it (and a constant timed function would also take the same time).