Below I’ve posted a link to a short (2 min) video of Tim Keller talking about his process for sermon prep (including number of hours per task).
My own process is very similar to his (though mine includes a lectio divina phase and doesn’t include quite so many hours), especially the part about significant time going into tightening and editing at the end. Some assume that pastors spend a lot of time on sermons in order to fill their content and/or time. For some, that’s true. But for me, it’s the opposite. My tendency is to accumulate too much content in a short amount of time. When I don’t put enough time into focusing, trimming, and editing my content my sermon almost always goes too long. So, somewhat counter-intiutively, I spend more time in order to be more concise.
Here’s the link to the Keller video: http://www.dennyburk.com/tim-keller-on-sermon-preparation/