Description
Returns the time to live left for a given key, in seconds. If the key doesn't exist, FALSE is returned. pttl returns a time in milliseconds.
取得一个KEY已经存在的时间。如果这个KEY不存在，则返回FLASE。PTTL使用毫秒为单位。
Parameters
Key: key
Return value
Long, the time left to live in seconds.
Example
$redis->ttl('key');
