How did they pray: set hours, set prayers, facing east?

Didache c. 100 ADDidache 8.1–3

Do not let your fasts be with the hypocrites: they fast on the second and fifth day of the week, but you fast on the fourth day and the day of Preparation. Nor pray as the hypocrites, but as the Lord commanded in his Gospel, pray this way: Our Father in heaven, hallowed be your name ... for yours is the power and the glory for ever. Pray this way three times a day.

The Lord's Prayer three times a day, with a closing doxology, and fasting on Wednesday and Friday.

Tertullian c. 155–c. 220 ADOn Prayer 25.1–5

As to time, there will be no idleness in outwardly keeping certain hours, I mean those common ones that mark the divisions of the day, the third, sixth and ninth, which we find more solemn in the Scriptures. The Holy Spirit was first poured on the gathered disciples at the third hour. Peter, on the day he saw the vision of the vessel, had gone up to pray at the sixth hour. He and John went into the temple at the ninth.

Tertullian adds the "lawful" prayers at the beginning of day and night.

Origen of Alexandria c. 185–c. 254 ADOn Prayer 32.1

Now a few words about the direction one should face when praying. There are four directions, north and south, west and east. Who would not at once agree that the east plainly shows that we should turn that way, symbolically, as the soul looks toward the rising of the true light, when we make our prayers?

Origen says one should face east even if the house's door opens another way.

Cyprian of Carthage c. 200–258 ADOn the Lord's Prayer 35

But for us, dear brothers, besides the hours of prayer kept from of old, both the times and the mysteries of prayer have now increased. For we must pray in the morning, so that the Lord's resurrection may be celebrated by morning prayer ... and again at sunset and the close of day.

Morning and evening, added to the third, sixth and ninth hours: the outline of the later daily office.

Basil of Caesarea c. 330–379 ADLonger Rules (Regulae fusius tractatae) 37

The appointed times of prayer in the brotherhoods must not be passed over, times which we have necessarily chosen... Dawn first, so that the first movements of the soul and of the mind may be offerings to God... At the third hour, to rise for prayer and gather the brotherhood together... reminded of the gift of the Spirit, given to the apostles at the third hour, to worship all with one accord... At the sixth hour we judged prayer to be necessary, in imitation of the saints... The ninth hour has been handed down to us by the apostles themselves in Acts as necessary for prayer... When the day is complete, thanksgiving for what was given us in it... Midnight was handed down to us by Paul and Silas as necessary for prayer... And we must rise for prayer before dawn.

Basil's rule for monastic communities (the Asceticon). Question 37 asks about the times of prayer; in the library's locked text the answer begins at the end of the preceding section, so the quote is drawn from sections 36 and 37 together. The day is framed by prayer at dawn, the third, sixth and ninth hours, at the day's end, at midnight and before dawn: the skeleton of the later daily office.