The Bible mentions no set times to pray or how often.
When our Lord needed to choose his apostles, he prayed all night. (Luke 6:12 “he went out into a mountain to pray, and continued all night in prayer to God.” ) So when we have important decisions to make or are troubled, we might desire to entreat the Lord all night. Though very few have the stamina to do that.
The Apostle Paul encourages us to “Pray without ceasing. In every thing give thanks: for this is the will of God in Christ Jesus concerning you.” (1 Thessalonians 5:17,18) Is this really possible? If, as Paul instructs in 1 Timothy 5:8, we are to work to support our families, how can we pray and work at the same time? Harmonizing the two scriptures and considering what is practical, we are to be an in attitude of having God’s will done in our lives and to have his guidance over us as we fulfill our duties. Additionally, we need to maintain an attitude of appreciation for all He has done for us. This would be more of an informal prayer that we should have in our minds at all times.
Some scriptures in the Old Testament suggest that the sacrifices of Israel connected with the Tabernacle and the Temple encourage Christians to pray as a minimum in the morning and in the evening. This is based on the morning and evening sacrifices of a lamb (picturing our Lord Jesus). “Thou shalt offer upon the altar; two lambs of the first year day by day continually.” Exodus 29:39 “The one lamb thou shalt offer in the morning; and the other lamb thou shalt offer at even” Ex 29:38,39.
David compares his prayers to these sacrifices:
“ LORD, I cry unto thee: make haste unto me; give ear unto my voice, when I cry unto thee. Let my prayer be set forth before thee as incense; and the lifting up of my hands as the evening sacrifice. “ Psalms 141:1,2
Daniel prayed three times a day. “he kneeled upon his knees three times a day and prayed and gave thanks before his God” Daniel 6:10
God enjoys our praying as a Father would enjoy the heartfelt appreciation and request of any of his children. We are privileged to come to our Father in prayer whenever we so desire.