A long time. Sort of like 18 years. At that time I was searching the net for information on creation and evolution. I ran into arrogant atheists and naive young Earth creationists. So I started my own little set of web pages to deal with the issues. Eventually I ran into the blockworld concept from modern physics and it was at that point I knew I had to do the book. Of course, if you understand the blockworld concept, it, in fact, took my whole life to write the book because a lot of preparation was needed. (At the time of publication, that would be 64 years.)