If the singers are over-scheduled, they could decide to drop your choir. Have you considered meeting with some of the best singers and outlining your problems. Ask them for advice and solutions. It's worth a try.

Provide dinner and wine after the rehearsal...

Usually, church choir rehearsal nights are Thursday or Wednesday - a given area will tend to stick to one of those, to prevent overlap with non-church choral groups (the rehearsal days for which tend to be Monday or Tuesday).

That said, given my daily schedule, needing to be up by 4AM and therefore needing to be home in the evening on "school nights" by 8PM, wild horses couldn't get me to join any choir that has a rehearsal on such nights so long as my schedule is such, which is for the foreseeable future. So, after more than a generation of singing in church choirs, I support congregational singing by being in what I call the retrochoir in the pews.

You will very likely lose choristers - and perhaps some of your best ones - by choosing to rehearse on weeknights. That doesn't mean it's not worth doing. It merely means you might have to significantly modify your programming.

It's all about triage.

"Many of the most difficult situations will not be shared with the likes of a choir director."

For The Win. Even many prosaic situations won't be shared.

Thanks for comments so far, I liked the one about the wine. At the mo we provide a cup of tea on the rare occasions when we do schedule a practice, (this is the UK) but wine might work better.
Sounds like a poll would be a good idea to find out what is the best night,
Someone commented to me lately on 'the curse of the volunteer'. People seem to feel they are doing the church a service by turning up when they feel like it, rather than seeing it as a privilege to serve the Lord by singing in the choir.

I'm not sure if my comments are germaine, but I will offer

A) In many local churches (here I may be speaking largely of Episcopal/Protestant churches, but this also holds true for a handful of Catholic churches in my area) the weekly rehearsal has been in place from time immemorial, and it is understood that joining the choir means committing to a weekly rehearsal. And I think a weekly rehearsal is essential (in addition to a good warm up and mini-rehearsal before the service)! Our group rehearses each of our 'major' weekly Sunday pieces (anthem, motet, etc..) for a minimum of four weeks, and rehearsal aids are available via our choir page on the church website so that my amateurs can review and prepare between rehearsals. For this reason, I can be flexible when folks need to miss an occasional rehearsal—they have had ample time with the music.

B) I think the specific problem of establishing weekly rehearsals (yes, please—do it!) should be viewed in the bigger context of building the choir program. Maybe that's a different thread. But (and I mean no offense, for I know the realities out there) a choir with a handful of members that gets together to rehearse things once before Sunday mornings, or even once a week, is probably not a choir that the local experienced, able singers would be interested in singing in. If you can create something that people will want to be a part of, weekly rehearsals and all else will fall into place.

I'm not saying it's easy, and it will take a commitment over time to establish. But dream big and go for it! Develop a vision and communicate it throughout the parish and community, using whatever and all media at your disposal. Get involved with the local secular choir groups, summer 'sings', possibly theatre groups if you do that sort of thing—i. e., go where the singers are, and get to know them! Establish yourself as a known local musical quantity (i. e. accompany every soloist or group in your area who asks you.) And above all, be GOOD! Learn from everyone and make sure that you are offering everyone (your singers, clergy, congregation, the Almighty) the very best product you can deliver!

In any event, good luck!

Our choir rehearsal is on Thursday, this does cause problems with the number of Feasts that fall on Thursday (We sing evening Masses in London on Feasts).

We chose Thursday as it was a free day,
Monday, Sung evening Mass.
Tuesday, N.O. choir rehearsal.
Wednesday, Sung evening Mass.
Friday, evening Masses at various places nearby most Fridays.

N.B. The Sung evening Masses are not at our own parish!

With the distances everyone is coming from, usually straight from work, it is only fair that we have dinner provided. Choir rehearsals are at my house but occasionally move to other members houses, tea /cold drinks are provided when people arrive we then have a 1 ½ hour choir rehearsal and then sit down for dinner. This term we have worked our way across Switzerland to the Alsace and on to Toul, having a different Pinot Noir each evening!

I have days when my choir sings beautifully - must be the Holy Spirit at work. I have days when directing that choir is like watching a train wreck but being powerless to stop it. There are a few "tricks" that have helped in rehearsing folks who can't easily make it to every Wednesday rehearsal. I scan scores and send them by e-mail, and have choristers who live near the sometimes missing drop in and help them with the scores. I also stay over after the Sunday choir mass and rehearse with singers I know can't make rehearsals. Like most these days, I do what I have to do.

Don9of11:
Choir numbers 17 in theory; usually on a Sunday we get about 12 as we did today. Ability range is wide too. We have 4 tenors, one is inaudible, one pretty good, one a choral scholar, one not bad but doesn't read music. Only one elderly bass but he is ex King's Cambridge and would be happy to attend week night rehearsals even tho he can sight read needless to say. I'm surprised but grateful that he comes at all.Three, occasionally four altos, not bad tho one is our oldest member so rather quavery. The rest are sopranos ranging from good to not very.
Their ages range from mid 70s down to 20ish. I'd say most are 40/50 ish. We have 4 choral scholars, full-time students who, because of the contract in existence when I took over, are not required to attend weekday nights anyway.

There are plenty of good choirs in the area, giving the opportunity to sing things like 'Elijah,' Brahms Requiem, madrigals, Gilbert and Sullivan, musical theatre, barbershop etc etc, though only our better singers aspire to this. In fairness some have to travel because of work etc, but there does seem to be a culture of turning up and expecting to sing irrespective of whether they've been to any rehearsals or not. Most don't see it as a vocation, rather that they are doing the church a favour by being there at all.

My solution such as it is, is to attempt only very undemanding music. That means they sound ok, but they think they are doing well. We could do so much better!
But there are probably lots of choirs like this out there!
I'm going to run a poll after Christmas to find the night that suits most (or maybe that suits the best ones) and go with that.

Sounds like a good plan Viola. I know how important it is to have every one at practice. Our small group of singers will be singing Psallite by M. Praetorius this Christmas. The psalm will be Today is born our savior by J. Chepponis. , we have other selections we are doing before Mass as well. We have another tenor joining us who is not from the parish but a friend of the Music Director as well as another Alto. We will have 8 if we are lucky.

I think in addition to your poll I would put all your cards on the table, shake the vine so to speak and let them know how you feel and what your pastor has said or perhaps he should stand with you. Anyway, the best of luck to you, will keep you in prayer.