It is amazing how much time it takes to work on a lecture. I am getting a lecture ready now I have given the last couple of years. So far I have probably spent 20 hours working on this already completed lecture. Reading new reviews of the area to see if there was anything new that I should incorporate, see if any figures were better than the ones I was using etc. A big part of getting the lecture ready is to make sure it flows and is understandable.