A consistent factor in the Christian biographies that I have read is a habit of regular, extended times of prayer. But this does not come easily. Most of us wish we lived closer to this ideal but more often find ourselves falling short of lofty goals.
In The Christian in Complete Armour, William Gurnall (1616-1679) offers simple and realistic advice on how to get closer to habit of regular, extended times of prayer. In a section on “watching to pray”, by which he means preparing for set prayer times, Gurnall says:
He doth not watch to pray that never thinks on God but when he is on his knees; for, by this long discontinuing his acquaintance with God, he indisposeth himself for the more solemn addresses of his soul to him. Long fasting takes away the stomach. The Christian will find that the oftener he is refreshing his spirit with those little sips and short gusts of heaven, the larger draught he will be able to take when he returns to his set meal of morning and evening prayer. For, by the means of these he will be secured from worldly affections, which exceedingly deaden the heart, and also be seasoned and prepared for further communion with God. These short walks often taken keep the soul in breath for a longer journey.II.502 in the Banner of Truth edition, 2013
To summarize: to pray longer (at set times)…pray shorter (all throughout the day).