Old telephone rings were loud. Jeremy was a young man not someone old and deaf. There are certain times within the sleep pattern where you can be wakened up more easily than at other times also.
As I've mentioned a few times,Jeremy on the lazy side anyway,so would have taken his time in answering,especially at that hour. I doubt he was one for rushing whatever he did,as he appeared to be a laid-back character,the same as he is now, otherwise his incarceration would have driven him insane if he'd been the type to have lived on his nerves. How strange that most criminals live on their nerves ! Because they are on the alert at all times,unlike dozy Jeremy, as he was in the early/mid 80's where people walked all over him.
Unless you can cast your mind back to the 80's,or earlier,I'd give up on the case if I were you. Times were a lot different than they are present day. You have to understand that era.