$nonce = round(microtime(true) * 100); code example

Example 1: php milliseconds

//Timing executation time of script
$startTime = microtime(true); //get time in micro seconds(1 millionth)
usleep(250); 
$endTime = microtime(true);

echo "milliseconds to execute:". ($endTime-$startTime)*1000;

Example 2: time now with milliseconds php

$d = new DateTime();
echo $d->format("Y-m-d H:i:s.v"); // v : Milliseconds