Did you include the time it took to read what was needed, including the different exceptions? I would estimate, if one wasn't fresh and up for a challenge, 15 minutes (against your approx 10 minutes). And given that a day of programming isn't pure programming, I'd double it to 30 minutes. It feels way too long, but it's a realistic, day-in-day-out estimation.

Programming takes time... which is why it's so powerful if you can reuse code (as Bloch did), and even better if you can find a way to reduce the code needed, or best, to avoid needing any code.