First I’ll give a summary, then some history, then finish with the Scriptures.
The Scripture does not say how long or short your prayers should be, but it does prescribe frequent prayer.
It is better to pray often than pray long. (Many periods of short prayer is better than fewer periods of long prayer.)
Pray as long or as short as you can or need to, but be concise and meaningful in your prayers.
Prayer alone is prayer; devotion, reading, Scripture recitation can all help one develop an attitude of prayer but should not substitute for prayer.
Benedict of Nursia: “Our prayers, therefore, should be short and pure, unless by some inspiration of divine grace it be prolonged.
Augustine believed that prayer must be “free of much speaking, but not of much entreaty, if the fervor and attention persist.” He preferred “very brief, quickly dispatched prayers.”
According to Thomas Aquinas, frequency, not length, is the important issue in prayer. “Frequent short prayers are of more worth than fewer lengthy prayers.” Earnestness and zeal are crucial so pray as long as you are fervent and stop when you become weary [or distracted].
Luther: prayer times should be numerous but short in duration. Rather than “mumbling the appointed hours” or “the babbling of words,” he prescribed “brief prayers” that are “pregnant with Spirit, strongly fortified by faith.”
Also from Luther: “The fewer the words, the better the prayer. The more words, the worse the prayer. Few words and much meaning is Christian. Many words and little meaning is pagan.”
Bloesch’s comment on Luther’s words: “The people of God will pray constantly but always with few words and profound meanings” (p. 60). [cf. 1 Thess. 5:17]
Luther also taught that prayer should be the first order of business in the morning and the last and night and advocated falling asleep with the Lord ’s Prayer on your lips.
Calvin urged that prayer be made when we arise, before we begin work, before we eat, after we eat, and before bed.
D. L. Moody: “A man who prays much in private, will make short prayers in public.” Moody thought lengthy public prayers were religious pretension.
Bloesch: “Lengthy prayers are not to be ruled out in public, but they are the exception rather than the rule.”
Some biblical and historical examples of long prayers: Jesus spent whole nights in prayer, David fasted and prayed for a week, Charles Simeon spent four hours a day in prayer and Luther at least three.
[It is interesting to note, however, that some of the significant prayers of the Bible are rather short, for example, Elijah’s prayer on the mountain (1 Kings 18).]
Bloesch: “What characterized the great saints was not so much involvement in one single protracted prayer or the endless repetition of prayer formulas as the practice of constantly waiting on the Lord, of praying inwardly even when outwardly occupied in daily tasks.”
Remember, Christians are not bound by ritual laws, but there are times that are appropriate for prayer: when we gather for worship, when we rise, when we lie down to sleep, and before meals so we eat with thankful hearts. Christians, should, however, feel free to pray anytime, anywhere (1 Thess. 5:17).
Pray as long as you need or want to but aim to be concise and put meaning behind your words and avoid vain repetition. Prayer whether you feel like it or not and try to cultivate the habit of prayer.
Some Scriptures that can guide us:
Don’t confuse long “speeches at God” with prayer: Matt. 23:14; Mark 12:40; Luke 20:47.
“Pray without ceasing” (1 Thess. 5:17).
Paul constantly interceded for his fellow believers: 1 Thess. 2:13; 2 Thess. 1:11; Rom. 1:9; Col. 1:9-12; Phil. 1:3-4; Eph. 1:16-19.
Pray with meaning: Matt. 6:7.
Pray in the morning: Psalm 88:13
Pray at morning, evening, and at noon: Psalm 55:17.
Pray seven times a day: Psalm 119:164.
Daniel prayed three times daily: Dan. 6:10.
Jesus prayed before sunrise (Mark 1:35) and in the evening when the day’s work was over (Mark 6:46).
Peter prayed at the sixth hour (Acts 10:9) and the ninth hour (Acts 3:1).
from Donald Bloesch, The Struggle of Prayer, 59-62.