If you want to set an absolute maximum execution time for stream_select in a loop, it's important to decrement the max_time value passed to stream_select.

<?php
// The maximum time for execution in milliseconds
$maxtime = 200000;
// The time the loop started
$starttime = microtime(true);
// Original array of sockets
$r = $orig_sockets;

// The function to calculate the timeout
function calctimeout($maxtime, $starttime)
{
    return $maxtime - ((microtime(true) - $starttime) * 1000000);
}

while (stream_select($r, $w = null, $e = null, 0, calctimeout($maxtime, $starttime)) !== 0)
{
    // loop through the sockets that showed activity
    foreach ($r as $socket) {
        // $socket talked
    }

    // stream_select modifies the contents of $r
    // in a loop we should replace it with the original
    $r = $orig_sockets;
}

?>