God gave us, humans, the three conditions necessary for living—breathing, eating, and moving. If any one of them is missing, how can we sustain our life? Those who are in the truth sustain the life of their souls as they breathe through prayer, eat the words of life, and move through preaching. Just as we must breathe continually to sustain our physical life, the Bible says that we should pray continually. The reason is that prayer is like breathing.
The main point of your question is related to the regular prayer time. In order to save us, humans, God established the heavenly sanctuary where sacrifices for the forgiveness of sins are realized. In that sanctuary, Christ who is the High Priest offers a spiritual sacrifice for us according to the regulations He established, and the spiritual sacrifice is His blood.
God already showed Moses the ceremonies of such sacrifices that are held at the heavenly sanctuary. God showed Moses the heavenly sanctuary and made him to build the earthly sanctuary as a copy and shadow, so that he could offer sacrifices to God. Therefore, the sacrifices legislated during the time of Moses were the copy and shadow of the true sacrifices that would be realized in the heavenly sanctuary. The Jews offered up sacrifices at the earthly sanctuary according to the Law of Moses, and during that time, the people prayed outside (Lk 1:8–10).
Besides the sacrifices that people offered with animals at the earthly sanctuary when they became aware of their sins, there were sacrifices offered regularly in the morning and at twilight, burnt offerings offered on the Sabbath day, sacrifices offered during the feasts at appointed times, etc.
The ceremonies of such sacrifices that were held at the earthly sanctuary serve as the copy and shadow of the true sacrifices that would be realized in the heavenly sanctuary, and they show us the times and periods when the sacrifices are made. Of course, in the heavenly sanctuary, the blood of Christ, not the blood of animals, becomes a sacrifice, and the prayers of saints reach the throne of God.
In the Old Testament times, sacrifices were offered up at regular burnt offering times and they served as a copy and shadow that Christ would be offered as the true sacrifice. In order to fulfill the prophecy, Christ was crucified at the third hour [9 a.m. at the present time] and died at the ninth hour [3 p.m. at the present time]. The third and ninth hours, when Christ, who became the true offering sacrificed in the heavenly sanctuary, was crucified and died on the cross, became the prayer times in the New Testament times, and during those hours, along with the sacrifice that Christ fulfills in the heavenly sanctuary, our prayers reach the throne of God.
The saints in the New Testament times pray at all times, keep the Sabbath and the feasts, and participate in the daily prayer times so that they can participate in the true sacrifices that are conducted in the heavenly sanctuary (Ac 3:1).
One more thing to be explained is that the time system used by the Jews in the time of Jesus is different from the time system we have today. Back then, they regarded the sunrise time as zero hour and the sunset time as twelfth hour. An hour in summer was more than sixty minutes, and in winter it was less than sixty minutes.
For this reason, the prayer times in summer are 9 a.m. and 3 p.m., and the prayer times in winter are 10 a.m. and 2:30 p.m.