一道选择 There are some health problems that,when ___ in time,can become bigger ones later on.正确选项是not treated但不明白为什么not having been treated不对呢我感觉treat和become 有时间上的关系 况且有一个later on,还有就是they are having been done与they haven't been done意思上有区别吗、、、

when (they are) not in time,状语从句、插入语中可以主语+系动词（必须同时省略）。甚至引导词也可以省略，如这里的when. 因为没有when they are not having been treated in time这中表达（having作助动词的时候是没有分词形式，只有做实意动词的时候才有），所以省略主语+系动词后剩下的when not having been treated in time.
状语从句的省略不熟悉的时候一定要还原成完整的句子，看是否正确，什么部分能够省略一定要搞清楚

这里只是描述句，用一般现在时态就可以了。
可以把原句改写为：There are some health problems that, when it is not treated in time,can become bigger ones later on.意思是有些健康问题如果没有及时对待，日后会变得更加严重。疾病是被对待，所以要用被动语态。

not having been treated 不是不对,而是不及not treated 精炼
没有they are having been done这种动词形式

后面不用管，首尾部分连起来看，中间是插入语修饰，problem 是被treat 所以是when treated 省略了be