Hundreds of hours coule be reasonable if you included conception, explorations of alternatives, etc... Just think of multiple designers being involved.
It's incredibly easier/quicker to code something when you're just copying someone else's end result.
I agree that it is reasonable, and the level of polish that they had in the final result is worthy of their time. I am sure that scrollkit has spent much more than 100s of hours creating the scrollkit toolbox and presumably the NYT did it from scratch.
I am mostly wondering where he got that number from, was it a guess, did they quote it at some point?
