In this case I'm talking about the tasks in each sprint. I think 1 day of planning per sprint is a lot. We are supposed to be agile. If we missed a task, swap it with another. If something isn't actually important, bring in something new. We end up doing this anyway... so why all the upfront planning each sprint?
Related back to the above comment, (my opinion) people really love to establish rules and processes and are not able to handle ambiguity. I spend a lot of time (remember the 4 hours a week) arguing whether a story is a mouse or a hedgehog.
IMHO it's splitting hairs, let's just do the work and we estimated a little wrong it just isn't that important.