Humble suggestion and example for my brothers in the pulpit - I learned from another Pastor's dissertation (Rev. Andrew Vandermoss) about oral preparation for preaching. 

Simply put, a sermon is a message spoken and heard rather than a paper that is written and read. As such, the suggestion that has helped me with the "land the plane" situation of "30 more minutes" is to preach my sermon, orally, out loud, sometime before the service in which it will be delivered. This doesn't mean you can't use a manuscript, or notes, or outlines, or passage overviews or any of those tools. By orally preparing you have a weight and a sense of the gravity and flow of the sermon as you prayerfully prepare (and orally practicing is a part of sermon prep). 

Much of the time my oral prep is 10-25 minutes longer than my actual preaching time on Sunday. I've found that on the weeks and occasions I'm not able to do this oral preparation my sermons are longer, and my transitions (such as statements about "in conclusion" or "to wrap up") are much less helpful. 

Early on in serving the Lord by preaching (almost 25 years ago) I wrote full manuscripts and stuck to them rigorously. Then I've used various tools, manuscripts, outlines, passage overviews, 4-part-paper-fold, PowerPoint slides, and a few others to support the work of preaching. However, I've never found anything to replace or replicate the importance of preaching the sermon first to myself. This oral preparation (accompanied by prayerful humble submission to the Lord, asking that even this preparation would be of kingdom use) has always been of benefit in the refining and delivery of God's Word to God's people. 

Also, side bonus, if you can prep in the place where you will preach, you become more familiar with your surroundings, be it open-air preaching, inside a church building, or in a prison. I've had visitors and church members stop by (not frequently, but occasionally throughout the years) and listen for a few minutes to a part of a sermon in preparation. I've heard from some (a few blue-collar industrial workers) that they were encouraged to hear and see that it takes "work to prepare a sermon" and that Sunday’s sermon wasn't just "a story you found on Google".