<?php
 
class Timer {
 
    const MICROSECONDS = 0;
 
    const SECONDS = 1;
 
    private $startTime;
 
    private $interval = 0;
 
    private $units;
 
    public function __construct($units = Timer::MICROSECONDS) {
        $this->startTime = $this->timeAsMilliseconds();
        $this->units = $units;
    }
 
    public function start() {
        $this->startTime = $this->timeAsMilliseconds();
    }
 
    public function restart() {
        $this->start();
    }
 
    public function elapsedTime() {
        $diff = $this->timeAsMilliseconds() - $this->startTime;
        if($this->units == Timer::MICROSECONDS) {
            return $diff;
        } else {
            return (int)($diff / 1000);
        }
    }
 
    public function setInterval($interval) {
        if($this->units == Timer::SECONDS) {
            $interval *= 1000;
        }
        $this->interval = $interval;
    }
 
    public function intervalElapsed() {
        return ($this->timeAsMilliseconds() - $this->startTime) > $this->interval;
    }
 
    private function timeAsMilliseconds() {
        return round(microtime(true) * 1000);
    }
 
}

require_once('Timer.php');
 
// timer test, milliseconds
$timer = new Timer();
$timer->start();
usleep(1000);
echo $timer->elapsedTime() . 'ms';
 
// timer test, seconds
$timer = new Timer(Timer::SECONDS);
$timer->start();
usleep(1000);
echo $timer->elapsedTime() . 's';
 
// interval test, milliseconds
$timer = new Timer();
$timer->setInterval(2000);
$timer->start();
usleep(1000);
echo $timer->intervalElapsed() ? 'true' : 'false';
usleep(1200);
echo $timer->intervalElapsed() ? 'true' : 'false';
 
// interval test, seconds
$timer = new Timer(Timer::SECONDS);
$timer->setInterval(2);
$timer->start();
usleep(1000);
echo $timer->intervalElapsed() ? 'true' : 'false';
usleep(1200);
echo $timer->intervalElapsed() ? 'true' : 'false';