Hard to say. I'm not a 'consistent' designer. I just work on levels on and off in my free time, when I feel like it. I don't know how many hours I spent working on 'Eurydice' but I think it took about a year to be made (I guess I could dig out my old laptop and find out exactly, but I don't think anyone's bothered enough to justify the effort).
The epic level I'm currently working on started in August 2010 and is now about three quarters finished. There were a couple of weeks last month that consisted of what can only be called fevered productivity and I made a huge chunk of level, including 2 cutscenes, three tilesets, the designs of a new area, several COs, two of the best-looking screens I've ever made, and a style of gameplay I've never done before, plus testing and updating the older parts of the level... but since then I've added a grand total 6 screens. I've set myself the target of having it finished before the end of the year.
Also, thanks for the comment and glad to liked it