It is true that by today's standards the time length would be as you say. In my days in college debate, 600-800 wpm was not unheard of (yes, it is virtually incomprehensible!). It is also true that we have been Steadily increasing the rate that we speak at. Notice the length of the sentences that Edwards and others used. It is comparable to the sentence length of the Greek New Testament (which, as you may no doubt guess, is quite long). It would require a slower pace in order to understand the speaker. You may also not be aware that Edwards was reputed to have had a speach impediment (i believe that he stuttered, though i may be mistaken about the particular malady).
Unless the published sermons have been edited for content, I don't think that Edwards would have been preaching for 3 hours non-stop. Many preachers today have 3 or 4 services every Sunday plus mid-week bible studies and they preach an hour per service. Is their dedication to be discounted? Are they less the servant of God than Edwards?
i have no idea what your sources are, so i would not be able to tell you whether they are abridged or not. My source is the late Dr. John H. Gerstner, a scholar of Jonathan Edwards, and the teacher of R.C. Sproul (both from Pittsburgh). i do not know how many services Edwards held at North Hampton and other churches, though because of the total length of service, i doubt that 3 or 4 would have been possible. i can tell you this: i have never heard any preacher do an expository sermon for an hour length. i have been in a variety of different churches in different traditions running from Assembly of God to Episcopalian, From Covenanter to Catholic, and a variety of "independents". Twelve to twenty minutes is the average. As per dedication, all i have to go upon is what God has given, namely the fruits of the ministry. That means i would have to look at each on a case-by-case basis, so i do not need to tell you that i will remain ignorant on that particular issue. Somehow though, i don't see a Great Awakening coming out of Saddleback or Willow Creek. All i see coming out of those places are 1) a Remnant chosen by God, headed for other places; and 2) a "dumbded-down" church that is afflicted by "God-lite".
Let us not forget that if you fell asleep during a Puritan sermon you could be flogged. There was an incentive to keep awake that you don't have in today's church. People today attend church because they WANT to, not because the have to. That was not always the case in the days of the Reformation and the days of Puritan America.
Many of the colonies such as Mass. had complete religious toleration, which meant that groups such as Catholics and Deists could exist. While in the 17th Century, church attendance was compulsory, this was not the case in the 18th Century. Franklin and Jefferson did not regularly attend, and many others could not for distance. Keep in mind that church buildings were often poorly ventilated, lit and/or heated with open fires in candles, lamps and stoves. Oxygen depletion was a problem and would be manifested in sleep. Indeed, these measures while seeming draconian, may have saved lives in an era where carbon monoxide was unknown.
Well obviously you've never heard Jon Courson. His expository sermons last at least an hour each and often as long as an hour and a half. It took him over 12 years to get from Genesis to Revelation and every sermon is here for your listening pleasure:
Jon Courson's Sermons at Firefighters for Christ
BTW why does a sermon have to be longer than an hour in order to be effective? God was quite short on words when he issued the 10 commandments. And I think that the average reader could read all the words in red in the entire new testament in about an hour. The Sermon on the Mount was about a 5 to 10 minute sermon. So the Lord does not judge the effectiveness of a sermon by the length, but by the content. So I would much prefer listening to a preacher who can effectivley communicate the gospel in a 10 minute sermon, than a preacher who rambles on for hours and hours and does not comminicate to anyone but himself. The length of a sermon is not how it should be judged. If so, then by that standard Jesus was a lousy preacher.