At what point of the Mass, when someone arrives after it has started, is it too late to receive Holy Communion? Is it OK to leave Mass after receiving Holy Communion?

Attending Holy Mass means accepting the Lord Jesus’ invitation to participate in His great Banquet sacrifice which unites Heaven and earth. It is responding to a King’s invitation to join him at a feast. Such an invitation means being there to eat a five course meal that includes the soup, the appetizer, the salad, the main entrée and the dessert. Would it be polite to arrive late? Would it be polite to tell the King that you do not care for the soup or the appetizer? Or would it be polite to skip the dessert and leave early? All of these behaviors would be rude.
 
To arrive late for Mass is not just a matter of fulfilling one’s Sunday obligation, it is an act of love and respect for the Lord Jesus who is gathering His children to share in the great moment during the Holy Mass when He will become physically present among the faithful. Each and every part of the Holy Mass is important, inseparable from one another. Prior to Vatican II, some theologians taught that arrival before the offertory was necessary to fulfill one’s Sunday obligation. The Catholic Church no longer supports this teaching. Its emphasis is now on the overall unity of the Holy Mass. The Liturgy of the Word and the Liturgy of the Eucharist are intimately united. Listening to God’s Word proclaimed in Sacred Scripture prepares the soul to receive the Incarnate Word of Jesus Christ in Holy Communion.
 
The second question is much easier to understand--Leaving right after Holy Communion is unacceptable: Where we have just received the Body, Blood, Soul and Divinity of Jesus, Our Lord, it is extremely disrespectful and shows others you may not believe in the Real Presence of Christ in the Eucharist. After Communion, we have a period of silence where the Body of Christ is encouraged to pray immediately after receiving the Eucharist. We pray prayers of thanksgiving and pray for help and assistance for the coming week. I like to call leaving Mass early the Judas Shuffle, because Judas left the eleven Apostles immediately after the Last Supper.
 
If you arrive late for Holy Mass, ask yourself with a sincere heart if you should receive Holy Communion. You be the judge of the matter before God. If sharing in the Lord’s Banquet means something to you, then you should be there from the entrance procession at the beginning of the Holy Mass to the final dismissal and closing hymn.