time2Units.php

 '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 = strtotime("2017-01-12 21:49:00"); // Some timestamp in the past
$now = time(); // Current timestamp
$diff = $now - $past;
echo '发表于' . time2Units($diff) . '前';

?>