PHP实现添加时间转为多少时间前

public function time($created_at)
    {
        $time = time()-strtotime($created_at);
        if($time < 5 && $time){
            $created_time = '刚刚';
        }
        if($time > 5 && $time < 60){
            $created_time = $time.'秒前';
        }
        if($time > 60 && $time < 3600){
            $created_time = floor($time/60).'分钟前';
        }
        if($time > 3600 && $time < 86400){
            $created_time = floor($time/3600).'小时前';
        }
        if($time > 86400){
            $created_time = floor($time/86400).'天前';
        }
        return $created_time;
    }