<?php
/**
  * 时间差计算
  *
  * @param Timestamp $time
  * @return String Time Elapsed
  * @author Shelley Shyan
  * @copyright http://phparch.cn (Professional PHP Architecture)
  */
function time2Units ($time)
 {
    $year   = floor($time / 60 / 60 / 24 / 365);
    $time  -= $year * 60 * 60 * 24 * 365;
    $month  = floor($time / 60 / 60 / 24 / 30);
    $time  -= $month * 60 * 60 * 24 * 30;
    $week   = floor($time / 60 / 60 / 24 / 7);
    $time  -= $week * 60 * 60 * 24 * 7;
    $day    = floor($time / 60 / 60 / 24);
    $time  -= $day * 60 * 60 * 24;
    $hour   = floor($time / 60 / 60);
    $time  -= $hour * 60 * 60;
    $minute = floor($time / 60);
    $time  -= $minute * 60;
    $second = $time;
    $elapse = '';

    $unitArr = array('年'  =>'year', '个月'=>'month',  '周'=>'week', '天'=>'day',
                     '小时'=>'hour', '分钟'=>'minute', '秒'=>'second'
                     );

    foreach ( $unitArr as $cn => $u )
    {
        if ( $$u > 0 )
        {
            $elapse = $$u . $cn;
            break;
        }
    }

    return $elapse;
 }

$past =8; // Some timestamp in the past
$now  = time();     // Current timestamp
$diff = $now - $past;

 echo '发表于' . time2Units($diff) . '前';
?>