Haddon Robinson in his article on Busting Out of Sermon Block gave some very helpful advice regarding how long he lets a sermon ferment in the short run:
Work on sermons in ten-day cycles
The purpose of a longer cycle is to provide simmer time. On the Thursday ten days prior to the Sunday I will preach, I do my exegetical study. I read the text and think about it till I hit a wall. Then I write down what is holding me up: What words don’t I understand? What issues can’t I solve? What ideas don’t make sense? If you can’t state specifically where your problems are, you won’t get answers.
Thus, ten days before I preach a sermon, I know what I need to be thinking about, which I do while driving the car, taking a shower, or laying awake at night. This also directs my reading. I know where the gaps in my understanding are, and I can more quickly find the answers. I can cull twenty commentaries in an hour if I know the key questions. Often, when I sit down to resume study the following Tuesday, the issues in the passage are much clearer. I wonder, What in the world was I so hung up about?
While I have always planned my preaching out for the year (or at least two quarters out), I have struggled with looking beyond the current week. I am going to try this and see if it helps. Do you do a similar thing?