Set apart certain hours for prayer

Calvin's Institutes (1559)
Book 3 of 4 - How We Receive the Grace of Christ

Chapter 20 - Prayer as exercise of faith and way we receive God's benefits

Sections 48-49 - Closing thoughts on Lord's Prayer

48. This prayer covers everything needful, and to pray for more is going beyond the Word.

49. We don't have to pray it verbatim; many other good prayers are found in Scripture. But the sense and summary of it should not change.

Sections 50-52 - Special times of prayer and perseverance

50. We need to have set times of prayer, to fight our sluggishness: "when we arise in the morning, before we begin daily work, when we sit down to a meal, when by God's blessing we have eaten, when we are getting ready to retire." Don't do this superstitiously, though. No prayer of ours should seek to bind God's sovereignty in any way, by what, how or when we pray. We should also pray when aware of others' adversity or prosperity.

51. Sometimes our prayers feel like beating the air to a deaf God. But "even though He does not appear, He is always present to us." Ps 22:2. We may not drive bargains with God or grumble, incurring God's wrath as He answers us - Numbers 11:18, 33.

52. God still hears us sympathetically (1 John 5:15) even if we never get the answer we want. Faith perseveres in prayer, through trial.