Single day threads stay shorter and alow sorting later for searching etc. Just a thought.Okay, just to let you know: I think things are pretty clear, and I'll set up the challenge formally on Tuesday.
One question that I'm still not entirely sure about: I found the ten-day threads in January quite nice to use - but we're quite a few people participating, so the threads may get pretty long. I don't mind that, but I'd like some more opinions on that.
Other than that, I'd like to thank everyone for their opinions and insights - and thanks for voting!