Would I be unreasonable to ask people to leave by a certain time on Christmas Day?

There's nothing wrong with setting new expectations this year as everything's different with kids in the picture, especially a baby. Perhaps eat earlier so guests still have a fair amount of time to relax afterwards.
Hard bitten socialisers/drinkers may take exception but they can move the party to their house if they want. Don't set a precedent of doing all the hosting - you may come to resent it! Reasonable people will be understanding.

I think it is totally reasonable! If you'd said you were worried about hosting on your baby's first christmas, I feel most posters would have advised you to set a time to leave as a compromise but as you've suggested that, everyone is telling you you are unreasonable! 🙃I would just say something in advance like "'please come from X until Y when we will be getting in our pjs 😁"

Surely with 2 kids in the house at least 1 person needs to remain sober? And by sober I mean under the legal driving limit

Make a (jokey but not jokey) invitation and put 'Carriages at ....pm' on the bottom.

I can’t imagine doing this. It’s really miserable and unwelcoming.

Why not take yourself off to bed if you’re very tired and let your guests enjoy themselves?

Its just 1 day. I would designate Boxing Day as total Us in PJs day. I would forewarn guests that you may be retiring up to bed as understandably more knackered with baby etc...but they are welcome to stay but quietly please.

YANBU. Ask your husband to handle the comms with his family. Sounds like your parents will be ok with it. I would possibly ask them to help you set the scene when the day comes too I.e. 5.30 'thank you daughter and sil it's been a lovely day, we'd better start making a move so you can enjoy some family time on your baby's first xmas'.

I host most Christmases. I never kick anyone out, so people stay as long as they like.
Boxing Day is mine though, so everyone knows I'm neither hosting nor visiting on that day.

But if you’re up early with a baby, then you’re cooking Christmas lunch/dinner for a big group, and being social as well as being mum, that’s exhausting! Not to mention that it’s dismaying to get up the next morning and find the mess and washing up from last night awaiting you. Perfectly reasonable to enjoy the company during the day but also want to tidy up and wind down in pyjamas before going to bed- it makes everything so much less fraught. Planning to include too much never ends well here, but it’s a lesson I’ve admittedly been slow to learn- fair play to OP to go for a day she can manage and that won’t bring its own hangover of resentment and recriminations on Boxing Day.

Or maybe it's considerate hosts ?

I don't think that's old-fashioned at all, and ideally you would.
If my social battery runs out at 5pm when he/the party can run until 11pm, it's reasonable he might want to stay longer and that's fine. Or you may work out a suitable middle ground.

I swear this thread is divided into considerate guests and CF guests 😂

I notice not many CF guests are saying if you’re invited to mine, stay as long as you like. They’re the ones saying don’t host then, I wouldn’t come, let your DH party on…😂

Your example is specific "come to dinner but we have an early start tomorrow". That is absolutely fine but completely different from saying it is the norm for social invitations to come with a fixed end time, as you suggested 👇.

Invitations to come celebrate from X to Y time are the norm, not some wild idea. I took my DC to a birthday party this weekend and none of the guests were offended that it was scheduled from 10am-1pm

If they pre-book taxis then absolutely give them an earlier time, and I’d think it’s easier to do so without sounding rude too - “we’re not planning to make an evening party of it this year, so suggest maybe booking taxis for 8.30ish?”

Its a tad party pooperish, it's only one eve - they'll all be dead one day, enjoy them now

Surely they have the common sense to leave at an appropriate time as you have a baby now? If they're not the thoughtful type then you need to give them a going home time.

I don’t think you can tell guests when they need to leave, no. If you feel like that, don’t host

yeah I dont get this either, whats wrong with that?

What kind of dickhead thinks its fine to get drunk and disorderly and stay up until all hours when a family has a new baby they'll likely have to get up with in the night.

I mean, to me that sounds reasonable - but it's obviously not to your collective family, who prefer to stay later, or to your husband, who seems happy.

You've got a child this year, so you could always make everyone aware that bedtime will be 7:30 or whenever and it'll need to be quiet downstairs after that point, but that doesn't necessarily mean they'll leave...

I think a proper invite might be the way forward, with a timeline like you get for a wedding reception. 12 - 1pm, arrive. 3pm Christmas dinner, 5pm Queens Speech, 7pm final toast, 7:30pm carriages type thing (I've absolutely made that up, obviously). Then people have a clear impression of what to expect, and when to plan to leave.

I'd also caution against having anyone over too soon - lots of friends warned us that they wish they'd had mornings opening presents with their little ones, and that people constantly arriving at various times and settling them in really distracted a parent, so I'd be planning quiet time in the morning to do presents with baby, and then expect people to stay until bedtime.

Why not?

I really can’t see why anyone invited for a catered Christmas lunch with their little grandchildren would have any issue ensuring they left at a reasonable and appropriate time, after helping as much as possible throughout the day.

Most wouldn’t need warning, they would do it naturally.

The problem drinkers in this scenario appear to be calling the shots.

You don't necessarily have to kick them out, but make it clear that baby's bedtime is x o'clock and so you will be having quiet time from then onwards, winding down, no music, "maybe just watching some films quietly, and then I'll probably have an early night too, what with the baby and everything, and if you don't like it you can piss off home".

But no, absolutely not unreasonable at all. Make it clear to them now though, so they can adjust/make other plans if they want etc,