That Peter prayed morning and evening may be assumed, for those were normal times of prayer. In addition he prayed at noon. Prayer three times a day was not commanded in the Scriptures, but Peter followed the example of pious men before him. Peter wentup to the roof to pray; this would have given him privacy. - Toussaint, S. D.
 Toussaint, S. D. (1985). Acts. In J. F. Walvoord & R. B. Zuck (Eds.), The Bible Knowledge Commentary: An Exposition of the Scriptures (Vol. 2, p. 380). Wheaton, IL: Victor Books.