function plural($num) {
 if ($num != 1)
  return "s";
 }
function getRelativeTime($date) {
  $diff = time() - strtotime($date);
  if ($diff<60)
   return $diff." 秒".plural($diff)." 前";
  $diff = round($diff/60);
  if ($diff<60)
  return $diff." 分钟".plural($diff)." 前";
  $diff = round($diff/60);
  if ($diff<24)
   return $diff." 小时".plural($diff)." 前";
  $diff = round($diff/24);
  if ($diff<7)
   return $diff." 天".plural($diff)." 前";
  $diff = round($diff/7);
  if ($diff<4)
   return $diff." 星期".plural($diff)." 前";
  return "on ".date("F j, Y", strtotime($date));
 }

分享文章：php返回相对时间（如：20分钟前，3天前）的方法
文章地址：http://hbruida.cn/article/psdjeg.html