Mine took place on a Saturday after Mass.

After (or between) mass(es).  The rite begins outside of the Church.

Does your chapel have more than one mass?  At our chapel, baptisms typically happen after low mass, before high mass-- if you only have one mass, my guess would be that it would be after, though obviously your priest would know for sure.  

Yes, I'm aware that it starts outside. I guess I was confused because of that. I wasn't sure about whether the mass started after the baptism was done. I plan on forming a small schola of all males (monastic! :), including myself, for the mass. I think it'd be great to sing for my little girl's first mass. I want to keep everything as traditional as possible; all medieval music.

This is very interesting.  I'd like to know what you find out.

I'd say ask your priest.  I have been in small groups who sang
some chant for infant baptism.   It would just be whatever the
priest says is appropriate.  All in all, I imagine that if the choir
was removed by distance, like in the choir loft or in a detached
hallway, they could just be singing all the time, background-wise,
but if you are the father and you want to be up close, that wouldn't
be practical.  So there would have to be certain moments when
you would step back and sing, then step forward and join the
ceremony again.  So the schola shouldn't be more than 10 feet
away, probably.   They should sing softly so as not to upset the
baby!!  (A crying baby at Baptism can be a bit of a problem.)


You might consider the following ideas for music:

Vidi Aquam (sung during ritual before Mass)

Sicut Cervus <--YouTubelink - Palestrina (most beautiful when
done very softly - If you have three Tenors and a Bass you
can transpose the Soprano part down one octave and keep
the Alto as is, with the Tenor part, and the three Tenors cover
those.)

Ubi Caritas<--YouTube link - Duruflé (Maurice Duruflé isn't medieval
but this work will knock your socks off!  Has parts for up to
5 voices - amazing! There is a YouTube of it being done in St.
Peter's Bernini Square last month, but the music quality is
TERRIBLE.  The conductor is an idiot, but the singers are very
good, just under incompetent leadership!)  

Ave Maria <--YouTube link, duration 2:30 sung by the Ave
Sol Chamber Choir. - composer: the incomparable Tomás
Luis de Victoria +1611

Panis Angelicus <-- YouTub link (Sopranos and Altos S-L-I-D-E a lot!)
- by Fr. Lambilotte - Again, not really midieval, but very, very
good for your situation!  Excellent example of a piece that the
Soprano AND Alto taken down one octave makes a WONDERFUL
4-part men's motet with CLOSE harmony!!  This piece is for the
Blessed Sacrament, but Baptism is really about the closest thing
to the Eucharist in all creation.  So it's not inappropriate.  But
musically, this (Panis) would be second to none for your
men's schola!


(If your singers have much experience with sacred choral
music, they probably already know these monumental works,
but what they may well not have considered is that men's only
choirs can sing them by taking the Soprano (and maybe Alto too)
down one octave.)




Linked above:  The Cambridge Singers, Sicut Cervus/Palestrina!

[youtube]https://www.youtube.com/embed/0yd5EE0hAB8[/youtube]

Cambridge Singers, directed by John Rutter.  I sang under his
direction and he said it was like "driving a Rolls Royce."  That was
a big compliment from a British national like him!

You know, I never even considered having the schola chant in the background during the baptism, as if it is some sort of background prayer. I really want to have a semi private mass (of course it would be open to the public) to be offered for my daughter after the baptism but the pastor of the church said that it is very uncommon and it would be considered a favour. In all honesty I do not see this request to be any different from a marriage/mass. The marriage takes place before the mass. Technically you can be married without a mass but that is rare. He suggested that I attend the NO afterwards. I respectfully declined his invitation and asked him to find another priest to offer the mass if it wouldn't be too big of a hassle.

I sure hope it goes through!

Thanks for the song suggestions. One song I really like is Inviolata. I've never heard it performed organum before...it might be interesting.