Enos may have broken a Nephite record for the longest prayer, but Moses apparently communed with Jehovah for forty days and forty nights on Mount Sinai (Ex 28:18). It is not so much the length of time that is important. What is important is the fervent, diligent, and earnest manner in which Enos prayed.
"'To every thing there is a season, and a time to every purpose under the heaven' (Ecclesiastes 3:1). There is a time to pray, a time to cease from prayer. There is a time to walk alone, a time to walk together. For Enos this was a time for perseverance in prayer, a time to wrestle with the Spirit until an answer came…It would be unfortunate if one were to suppose that the experience recorded herein- as to both the tenacity of his spiritual quest and the response of heaven-is common to or typical of daily prayer. 'Never at any time have' our prophets and Apostles 'taught or endorsed the inordinate and intemperate zeal that encourages endless, sometimes day-long prayers.' (Bruce R. McConkie, "Our Relationship with the Lord," p. 103.) Times of pentecost and other spiritual outpourings are the more treasured because they are not a part of every day." (McConkie and Millet, Doctrinal Commentary on the Book of Mormon, vol. 2, p. 97)
Harold B. Lee
"I once read that scripture to a woman who laughed and said, 'Imagine anybody praying all night and all day.' I replied, 'My dear sister, I hope you never have to come to a time where you have a problem so great that you have to so humble yourself. I have; I have prayed all day and all night and all the next day and all the next night, not always on my knees but praying constantly for a blessing that I needed most.' (Stand Ye in Holy Places: Selected Sermons and Writings of President Harold B. Lee, p. 246)
Vaughn J. Featherstone
"Mental wrestling can take the form of prolonged prayer. It may be necessary to pray longer and harder sometimes in order to get the feeling that you have been heard. You remember the case of Enos and his day-long prayer. Of course, that was an extreme case involving a future prophet of God. If you ever get where you need to pray all day long, you will know it and the power will be given to you. It isn't the sort of thing you just set out to do because you would like to hear a voice like Enos did. Still, Enos's example is one you should ponder as you think of gaining the determination to think and communicate with God." (Commitment, p. 30)