The first chapter? Its taken 5 years to write the first chapter?
Its taken my whole life until now to write the first chapter, and the book.
When I talk of writing I chiefly refer to two things: rewriting and organization. Up until now I was assembling and abstracting data sets. Now its mostly rewriting and organizing it all.
As far as putting my "pen to paper" the vast sum of the first chapter was written in a day.
Large sections and layouts of the remaining text are already done, but I'm releasing this to certain individuals on a case by case, chapter by chapter basis. As such, I have to finish the first chapter to what I feel is a suitable level of work.
Also of note is that the first chapter is newer material (to me) and has less age than much of the rest of the work. As such it requires greater thought.