I let them. Often. In desperation, I can get a lot of work accomplished in a compressed amount of time. Unfortunately, this tactic has be successful for me nearly always. Thus, my mind rationalizes that I can procrastinate tasks up until the critical hour.
It doesn't help that advanced preparation on my part has often not paid off. Starting with the summer leading up to my second year as a teacher, I have found that the summers that I spend the most time preparing for the following years' classes are the summers before the school year when all of my classes will suddenly change. In a form of Murphy's Law, the classes I prepared for the most are the ones most likely to disappear. This has happened for the majority of my years teaching.
It similarly happened with my dissertation. I had nine months of working towards a particular direction with advance work on the following steps only to have it all have to change due to one review. It makes it difficult to work on it even though I know that time (and money) is trickling away.
In this sense, I look forward to each school year as I tend to be more focused with time constraints than I am with an open vacation schedule. I have a lot on my plate again this year, but that might be a good thing. I might be able to make better use of my time.