对于这个问题阐述一下我个人的观点：首先，您上面所提及的英文例句中在我看来没有一句是定语从句（非限定性）。

1.The fire lasted for 5 hours, during which time everything was destroyed.

2.I will never forget the day, on which time I first met you.

3.He will put off the picinic until May 1st, on which day he will be free.

4.I told them the reason, for which reason I didn't come.

5.They went to London, in which place they lived for 6 months.

问题出在哪里了呢？which 的词性上。绝大多数人认为 which 在这里是个关系代词，我对这种看法并不认同，我认为 which 在这里就是个指示限定词，如：this、that 等，跟定语从句（非限定性）丝毫无关，而是介词短语作状语仅此而已：

1. during which time （作状语表时间）

2. on which time （作状语表时间）

3. on which day （作状语表时间）

4. for which reason （作状语表原因）

5. in which place （作状语表空间）

在此之前也有老师回答过诸如此类的问题，都以非限定性定语从句作为最终解答，在此我保留个人意见。