He admitted that it took… Or, He admitted having it

Consider the following example:

A man wrote a book in 2 days. He admits it.

Should I say:

1. “He admitted that it took him 2 days to write the book”
2. “He admitted that it had taken him 2 days to write the book”
3. “He admitted having it taken 2 days to write the book”

Answer

Number 3 would more idiomatically be “He admitted it having taken him 2 days to write the book.”

(Apparently the system understood # as introducing a headline. Odd.)