YANBU OP. You are not wrong to want an answer from your MIL. Christmas takes a lot of organising for some. And is a stressful time for some too.
@Pippa999
Well then if that's the case you say 'I won't get my shifts for the Christmas period til 15th to 20th of November, (for example,) so I will let you know whether I am coming Christmas day or not by the 20th November.
Just be courteous and considerate and don't keep people dangling, like you and your time is waaaaay more important than them. Keep them updated, with what is happening and let them know as soon as possible.
And
@OrdinarySnowflake
And agree - "I can't say yet because I don't know when I'm working over Christmas, but would love to come if I can, I'll let you know as soon as I have my shift rota" = not rude.
Agree with these. I have family members and friends who won't know their Christmas rota til 3-5 weeks before, so like the last week to 10 days of November. One doesn't get it til 1st December. (They're a mix of emergency services workers, hotel staff, and starbucks and maccie D's workers.)
So all they have to say (for example) is 'I will know what days I am working in the second half of December on the 25th of November, so I will let you know if I can come on Christmas day, on the 26th of November.' (For example.)
I don't think that is too much to ask. As Snowflake said, just messing people about and keeping them waiting just in case something better comes along is very inconsiderate. I am sure that most people will know whether they are working Christmas day/boxing day, quite a few weeks/a month or more in advance. And as has been said, just tell the host that you cannot give an answer yet, but will do on 1st December/whatever date.
That's all anybody wants really, (even stressheads, and super-organised people who suffer anxiety.) Just be kind and thoughtful, and give them a date when you will have an answer for them if you don't know yet... No need for personal attacks against people who do things differently and like to be organised and prepared 6 to 8 weeks in advance, (And remember they quite possibly suffer from anxiety and stress and that's why they need to know asap so they can sort everything.)
@inghamsitaly
I am with Pippa* Georgie et al, I would want to know in advance not because it makes much difference to the size of the bird but because I just need to know in my head who is coming, who is staying, who I need to cater for and who I need to find a bed space for - hardly much to ask for an answer is it?
I agree with this too. It really is rather rude and inconsiderate for people to think it's OK to not give and answer and just string people along until it suits them. These people (inviting you for Christmas,) are being kind enough to be your host for the day (possibly 2 days!) and cook for you. Be more thoughtful, and think about someone else other than yourself. Honestly, it makes me wonder how and why these people are invited anywhere!
And no, it's not too early to start organising Christmas. It's November FGS. The restaurants and hotels and suchlike start taking bookings in August. Some even in July. So why someone considers early November to be too early is beyond me!