Needed time to chew on the challenge idea, to think of how to package and present it and to make sure it's pitched at the right level.
Have fun :)
(edited: At last, there's one challenge that can't be solved in 15 mins or half an hour. Because if every challenge can be solved so quickly, then we've failed to make them challenging ;))
(edited2: The earlier challenge, while doable, was unfairly hard due to a tiny bug. It's been fixed.)