Hours or points for sprint planning seems to be quite an opinion splitter in the Scrum community. Even the Scrum heavyweights Mike Cohn and Jeff Sutherland have chipped in with their opinions with both landing on either side of the argument.
I’ve discussed this a few times on the Scrum Alliance LinkedIn group and whenever I put my point across I’m not sure if my point has ever really come across. To be clear I always estimate stories in points (i’ll save the reason why for another blog) and always use story points for velocity calculation. I then always break tasks into hours. At the start of any sprint planning session I will always show the team their historical velocity for the last few sprints (no more than 5) and ask the team if there is any known absence for the next sprint. At this point I will ask the team what they think they can achieve in the coming sprint. The Product Owner should know the teams velocity and should have a good idea of what this team usually achieves in points to help them decide what to bring in.