When did the gathered church stop singing choruses?

This varies by denomination. Some don't have any music at all. Some have a whole lot of music.

As a Latter-day Saint, we sing at the beginning and end of each meeting, and usually once somewhere in the middle.

As Peter Turner said in his comment, they still do this in the Catholic church. When each separate church was founded, they would tend to make this sort of decision about whether or not they would sing in their meetings, and how often.

Perhaps some early Christians sang choruses at the beginning of worship, but this was not a standard part of the order of worship.

New Testament

From the beginning, worship was centered around the Eucharist.

The New Testament does not contain an order of worship, but Paul mentions worship practices in a few of his letters. He talks about worship songs in two of his letters (see Ephesians 5:19 and Colossians 3:16), but he says these are things we should do at all times, not specifically during the weekly gathering. When Paul does speak explicitly of the worship gathering (e.g., 1 Corinthians 11:18-26), he focuses on the Lord's supper.

For, to begin with, when you come together as a church, I hear that there are divisions among you; and to some extent I believe it. Indeed, there have to be factions among you, for only so will it become clear who among you are genuine. When you come together, it is not really to eat the Lord's supper. For when the time comes to eat, each of you goes ahead with your own supper, and one goes hungry and another becomes drunk. What! Do you not have homes to eat and drink in? Or do you show contempt for the church of God and humiliate those who have nothing? What should I say to you? Should I commend you? In this matter I do not commend you!

For I received from the Lord what I also handed on to you, that the Lord Jesus on the night when he was betrayed took a loaf of bread, and when he had given thanks, he broke it and said, "This is my body that is for you. Do this in remembrance of me." In the same way he took the cup also, after supper, saying, "This cup is the new covenant in my blood. Do this, as often as you drink it, in remembrance of me." For as often as you eat this bread and drink the cup, you proclaim the Lord's death until he comes.

Second Century

The Didache, a late first or early second century document, gives these instructions for worship:

Chapter 14. Christian Assembly on the Lord's Day. But every Lord's day gather yourselves together, and break bread, and give thanksgiving after having confessed your transgressions, that your sacrifice may be pure. But let no one who is at odds with his fellow come together with you, until they be reconciled, that your sacrifice may not be profaned. For this is that which was spoken by the Lord: "In every place and time offer to me a pure sacrifice; for I am a great King, says the Lord, and my name is wonderful among the nations."

The Didache also includes specific prayers to offer before and after taking communion, as well as guidelines for how to act toward itinerant preachers and prophets who speak to the congregation. But it does not mention singing.

Justin Martyr, in his First Apology, describes the typical Christian worship of his day:

CHAPTER LXV -- ADMINISTRATION OF THE SACRAMENTS.

But we, after we have thus washed him who has been convinced and has assented to our teaching, bring him to the place where those who are called brethren are assembled, in order that we may offer hearty prayers in common for ourselves and for the baptized [illuminated] person, and for all others in every place, that we may be counted worthy, now that we have learned the truth, by our works also to be found good citizens and keepers of the commandments, so that we may be saved with an everlasting salvation. Having ended the prayers, we salute one another with a kiss. There is then brought to the president of the brethren bread and a cup of wine mixed with water; and he taking them, gives praise and glory to the Father of the universe, through the name of the Son and of the Holy Ghost, and offers thanks at considerable length for our being counted worthy to receive these things at His hands. And when he has concluded the prayers and thanksgivings, all the people present express their assent by saying Amen. This word Amen answers in the Hebrew language to genoito [so be it]. And when the president has given thanks, and all the people have expressed their assent, those who are called by us deacons give to each of those present to partake of the bread and wine mixed with water over which the thanksgiving was pronounced, and to those who are absent they carry away a portion.

Again, there is no mention of choruses.

But singing is mentioned in a letter from the Roman governor Pliny the Younger to the Emperor Trajan. Pliny had been investigating an anonymous document that accused local Christians of subversive practices. Upon questioning the Christians, Pliny found the truth was more innocuous.

They asserted, however, that the sum and substance of their fault or error had been that they were accustomed to meet on a fixed day before dawn and sing responsively a hymn to Christ as to a god, and to bind themselves by oath, not to some crime, but not to commit fraud, theft, or adultery, not falsify their trust, nor to refuse to return a trust when called upon to do so. When this was over, it was their custom to depart and to assemble again to partake of food--but ordinary and innocent food.

Third Century

The Apostolic Tradition a treatise by Hippolytus of Rome, includes several liturgies for worship and church life. The only mention of singing is in chapter 25, following a community dinner.

After the meal they shall get up and pray, and the children shall sing songs, along with the virgins.

Summary

I have not been able to find solid evidence that singing choruses at the beginning of worship was widely practiced by early Christians.