Aaron, if you r reading this, how long did it take to make your programs?
It's hard to say for sure. The original one took the longest trying to figure out how the files were put together. I'm sure I spent two or three weeks getting the file formats down in GK. That's maybe a few hours per day looking at it. The UI in GK was pretty basic so most my time was spent on the analysis.
For DK/SK I had the file structure from GK to work with. There were some small differences but nothing hard to work with. I spent all the time I saved on the UI though. I spent easily 2 or 3 weeks on just the UI for DK/SK. But SK grew from DK and has a lot more stuff in it, so again it's hard to pin down how much time. I've worked on SK on and off for quite a while. Also with DK/SK I used the file format hacking project to get some insight into how the rest of the files were built. That probably took me a week or two to create the code that would allow me to navigate the game's resources -- to pull up the descriptions, icons, portraits, etc...
In the end, I don't know how much time, but it's a significant amount.