Now Peter and John went up together into the temple at the hour of prayer, being the ninth hour. . . (Acts 3:1).

"The hour of prayer": how foreign these words sound in the midst of our informality! Even Jesus, when asked how to pray, responded with a pattern of words that could be repeated with regularity (Our Father, who art in Heaven . . . ). Such "formality," employed with moderation, builds habit and discipline, and can put us in remembrance of God. Such an "hour of prayer" is commended by Andrew Murray, C.S. Lewis, George Mueller, and was the practice of the early church. The best testimonial though will come from your own experience. Set aside one, two or three periods in the day when you will utter a simple prayer. You may combine this with "informal" prayer and Scripture reading if you like. You might choose a special place, a closet (Matthew 6:6), so your mind can be trained to put aside distraction.
The formal and informal have an important relationship to each other in our spiritual life. An art gallery has walls that remain the same all the time, designed to display art that varys each week or day. The formal elements of our spiritual life, such as regular time we set aside for prayer, can contain different petitions, moods and readings depending on our momentary need. We need the permanence of these spiritual walls to accommodate the changing pictures of our spiritual lives. Although we may eat different food each day, the body digests better when meals are taken at regular times. The permanence and regularity can facilitate convenience and spontaneity.
God, save us from an exaggerated fear of regularity!