There are very few subjects over which preachers receive more criticism than the length of their sermons. Ezra read the Book of the Law to the people "from morning until midday" (Neh. 8:3), and while at Troas the apostle Paul preached a sermon and "continued his message until midnight" (Acts 20:7). However, the vast majority of sermons recorded in the Bible could easily be preached in under ten minutes.
When people ask me how long I preach, I usually respond, "Until I get done." I am not trying to be flip about the subject, but the length of a sermon depends upon the topic. I don't know how one could do justice to the story of the crucifixion of Christ in a 20 minute sermonette.
I've heard older preachers harshly criticize younger men for not preaching long enough. Sometimes this criticism is just -- other times it is simply an attempt by a long-winded preacher to justify himself.
Preachers usually don't like to admit it, but long sermons are often the result of poor sermon preparation. When preachers fail to do adequate sermon preparation you are apt to here a lot of tired stories about their youth, some worn out attempts at humor and very little Scripture.
During our years in Zion, I have prepared printed sermon outlines which are passed out to the audience before every sermon. Brethren sometimes joke about the length of the outline -- a four page outline usually means a short sermon. The reason is that a longer outline is the result of a great deal of preparation in which words can be chosen with more care, and extraneous material can be omitted. When the outlines are passed out and the brethren see less than a full page of notes, some of them wonder if they are going to have to cancel their dinner plans!
Another factor to consider is the speed at which a preacher speaks. I know of several preachers who could cut the length of their sermon in half if they would simply speed up their rate of speaking -- as an added bonus their audience might even be able to stay awake during the sermon!
I am reminded of the man who went to the dentist to have a tooth removed. The patient inquired as to the cost for removing a tooth and the dentist told him it would be $90. The man told the dentist it seemed like a lot of money for a few seconds work. The dentist told his patient, "Well, if it would make you feel better, I can pull the tooth out real slow!" I feel the same way about sermons -- if you think I preach too short of a lesson, I could just slow down my rate of speaking.
Many years ago brother Roy Cogdill debated D. N. Jackson, the great Baptist preacher. When the debate was transcribed and put into book form, brother Cogdill had to explain in the introduction that while both speakers had the same amount of time allotted in their speeches, in the book Cogdill's speeches took up twice as many pages -- the reason was Cogdill spoke rather quickly, while Jackson was about as slow as molasses.
The length of a sermon is not nearly as important as the content. Those who truly love the Lord will be willing to listen to the Word of God proclaimed regardless of how long it takes.