Grammar

I have some questions as they relate to some grammar.

By the time Alex finished his studies, he had been in London for over eight years.

Now I know that this sentence is in the Past Perfect but I also know that many times we can arrange sentences differently.

Here is another sentence but it has been rearranged.

Alex will have been in London for over eight years by the time he finished his studies.

This sentence contains the grammar necessary but appears incorrect to me. When the expression

by the time

is used, this second sentence appears incorrect but if I write the same sentence slightly different using the word

before subtituting by the time the sentence seems to be correct.

i.e. Alex will have been in London for over eight years before he finished his studies.

Can someone help clear up these sitations for me.