For the TLM, you must do the Introit. If it is the principle Sunday Mass, there should be the Asperges (or Vidi Aquam) before the Introit, and the procession before that, so during the procession you would need to sing something, or at least have the organ play, if you don't want silence. Even for Masses where there is no Asperges, there is usually still time to do a couple verses of a hymn during the procession, then the Introit during the prayers at the foot of the Altar, and the Kyrie during the Incensing (roughly speaking).

For the OF, I have no idea.

For nearly three years now we have used the texts offered at antiphonrenewal.com for the “entrance antiphon hymns” (I make worship aids so this is very easy to facilitate). We sing the hymn up to the doxology and then chant the Fr. Weber antiphon right after (which, subtly, counts as our repeat of the antiphon). It works very well. As you mentioned, it works best when there is incense, but we only do that when choir is in season, so when choir is not in season, the priest just goes to the chair and waits a moment while the antiphon is chanted. It’s not really any different than waiting while verse 4 of a hymn is finished; the only real difference being that a cantor is chanting rather than the people singing. I personally see absolutely no conflict between the rubrics and this practice. In fact, I think it a vast improvement over just singing any old hymn and ignoring the propers. This permits people to sing the propers, and then hear actual chant (preferred option) as well. It’s win-win. It’s also a great way to acclimate people to chant (in general) and draws a clear relationship between what the people have just sung, and an “official” rendering (the changed version) of that important text as well.

On the unofficial suggestion of a Bishop’s Commission member (who knows and follows the rules) we adopted this practice (for the Novus rite): once the introit, then a hymn during the procession, then the introit antiphon again possibly with verses if incense.

This adds to the win-win above, that this way the Mass begins right in with sacred singing. The difficulty perhaps is finding hymns that are appropriate, processional, and able to be stopped after not all the verses.

My understanding is that places that program a hymn before the (Latin or vernacular) Introit do it with an understanding that it gathers the people in anticipation of the opening clause of No. 47 of the General Instructions - that, having completed the hymn, the people have been gathered together.

Even the office of divine worship expressly permits this. See here

https://www.chantcafe.com/2012/02/the-usccbs-divine-worship-on-hymns-and-proper-chants/

These are great, well-reasoned methods you all have! Here we forgo entrance hymns in favor of the proper chants (OF). This has yielded a few unexpected benefits:

-- The people's singing of the dialogues (which was already good) is improved
-- It highlights the importance of the Gloria and Gospel Acclamation as high moments for the people's external participation.

Causes for the above effects:
-- Having people sing less improves what they DO sing.
-- After blowing all their steam on a huge opening hymn, who has energy to sing the dialogues and acclamations anyway?
-- People grow accustomed to having their own roles for singing in contrast to the parts that belong to the priest, deacon, choir, etc.

I have to agree wholeheartedly with btodorovich87. The "Entrance Hymn" always struck me like an "overture" to a big performace (opera?), and it tends to be "big" no matter the day or season, lending a sense of routine and monotony. A "smaller" choral entrance can be a better preparation for Mass, and prevents a "crowding" of Big Pieces all at the front end of the liturgy.

Veritas, how does flowing from the antiphon into a metrical hymn tune work? Can you provide an example score or recording?

The "Entrance Hymn" always struck me like an "overture" to a big performace (opera?), and it tends to be "big" no matter the day or season,

This is something I'm careful to avoid. We regularly use chant melodies for our entrance hymns (Jesu Dulcis Memoria, Veni Creator, etc.)

I have programmed the entrance antiphon about 1/5 of the time during the past liturgical year; the other 4/5 of the year I program a hymn. Introducing chanted entrance antiphons is new to my parish.

I use Fr. Weber's "The Proper of the Mass", most frequently his (iii) (Gregorian psalm tone) option, but occasionally the (ii) (medium difficulty) setting if it isn't that difficult. Occasionally I have thought that Adam Bartlett's entrance chant from the old "Lumen Christi Gradual" was better, and I have used that, for example, on Epiphany.

Sometimes I re-set the antiphon's text myself to a Gregorian psalm tone if I think Fr. Weber's setting has too much recitative.

My church has projection screens, and I create a slide with the antiphon's text and chant notation to display. The intent is for the assembly to sing the antiphon along with the choir, with the choir singing verses itself. Here is an example of a slide from the Transfiguration of the Lord:



We also chant the Communion antiphon at the start of Communion at every Mass. The assembly has been better about singing that antiphon than the entrance antiphon, but the participation is still not as robust as it is for familiar songs. Some people prefer to listen to the antiphons being chanted. It's still considered an oddity by many people, and I realize it will take time to shift people's expectation that Mass begins with a rousing song.

Serviam, here's my score for this week (Missa V). Luckily the antiphon fits in with 4/4 here, but if it doesn't I just add in an extra 3/4 bar and it sounds just like many of the irregular meter modern hymns. Or I change the rhythm to fit it in (Missa IV).

We haven't been doing this for very long though, and if the experiment fails I might try just having the antiphon, as chant, at the end.

It sounds like we've confirmed that this is a licit practice. I began the process of introducing the proper antiphons last year, during Lent. My parish has the four-hymn sandwich firmly entrenched in its culture. I didn't foresee doing away with the Entrance Hymn as an option, and we unfortunately don't use incense enough to plan the Introit around it, so I settled on singing the Introit during the five minutes prior to the ringing of the sanctuary bells and the start of the Mass. I also sing the Communion antiphon at the beginning of communion, while the EMCH's receive the Eucharist.

I've had a warm reception to the practice, and I've noticed some unplanned benefits:
- Prior to implementing the Introit I would play an organ prelude, and had the unfortunate problem of having parishioners (and even my own choir members) talk over it, using the sounds of the organ as a veil for their conversations. I've found that the talking issue prior to Mass has been entirely eradicated when singing the Introit. My theory is that people have been conditioned to consider instrumental preludes to be mere background music, but not so for sung music.
- Congregational singing of hymns has flourished. While many other factors influenced this, it seems hearing an unaccompanied voice prior to the start of Mass helps to "prime" people to sing.

It surprised me how many people, especially folks in their 60s and 70s who I would've assumed had experienced at least some of the old traditions, are simultaneously appreciative but unfamiliar with Gregorian chant as a whole. I've had to develop an "elevator pitch" explanation of what the proper antiphons are (Do you have a Missal? It's in there. The Church teaches...), what language I'm singing other than English (Latin is actually still the liturgical language of the Church), etc.

I use Fr. Weber's propers because they often utilize the same melodic structure of the antiphons from the Graduale Romanum. When Fr. Weber's propers and the GR line up, I sing the Latin antiphon from the GR and then the corresponding English antiphon from Fr. Weber after.

I'm hoping to begin training our choir and cantors to sing the simpler English Fr. Weber settings. Long-term, if we're able to switch from our Gather hymnal (customary groan) to a resource that has a congregational antiphon setting, I hope to introduce the parishioners to singing the antiphons.