To think this is rather rude?

I think it is because if you are organising things then those last 30 minutes are when everything comes together. If sil arrives at 4.30 and they have to stop, open the door and exchange a few pleasantries then those 30 minutes will be lost. Then guests start to arrive and there are things unfinished or those 30 minutes are the time that they want to get ready/shower/dressed/hair and make up etc in peace

OP cares, because they specifically said after 5 because that is when it is convenient for them to start receiving guests into their home. If you don’t live there and are visiting you are a guest, regardless of whether you are family or not. Check in time is after 5pm. OP’s house, OP’s rules.

I think it's rude to arrive early (and late, of course).

I an always punctual but that means being early, so I just find somewhere to sit in the car or in a cafe if travelling by train with a book until it's time to go.

I have a friend who makes a habit of arriving for things at mine about 20 mins early, and until I got wise to her I sometimes ended up hosting in my Cinderella rags because that last 20 mins was the 'me time' to get changed and brush my hair.

I think it must be mainly people who've never hosted.

You clearly have other beef with her. Don’t let it cloud your judgement. Just say no one will be home until 5.

I suppose if it's your party (DH doesn't like socialising), you want to be there to welcome your guests, and not leave them standing about on their own or trying to make small talk with someone who's socially awkward. We live in a part of the country where if you say "From 7pm" then most people won't turn up before 9pm!

Yes its rude, but I wouldn't respond.
You have stated 5pm.

I wouldn't arrive back until exactly at 5pm, she can sit in her car, not your problem.

Why? Your husband could have sorted them out and you could have continued with what you were doing. Genuinely asking rather than being goady. If he had something he was doing too he could have said you are a bit early and Nikita will be down in due course.

There wouldn't be an issue if SIL did as told an arrived on or after the time stated by op, if she wants to come earlier then SIL needs to ask or explain why she doesn't get to dictate the time she wants to be there.

It's rude after to think you get to override the arrival time given by someone, especially if it is at their home, no manners at all.

So have you replied that you won't be in, or not?

Surely if so then job done and no issue...

I wonder was that her way that she wants to talk to you or your dh about the relative before everyone else arrives. Honestly I would just ring her and tell her that you will not be in until five. Problem solved,

Depending on personality, and I suspect it’s not good as you are taking umbrage, she’s either helpful on pushing boundaries to tell you she is more important. So the choice is to say nothing and make it home for 5 and let her wait… or tell her in return you won’t be home at that time… I’m petty so I’d go with option 1 😂

Some of these suggested responses here are ridiculously formal for family

If this was us I would just be replying sorry SIL no one will be home until 5 but if it’s easier for you to leave home earlier then you might want to find a cafe on the way

I wouldn’t think it’s rude, I would just assume that works best for her travel wise

Sounds like it’s going to be hard enough to talk about the topic of care without getting worked up about things like this

She wants to be first in so she dominate the decision making process.

Unless they thought they might be helping you set up the table, food, bar etc it's definitely rude to arrive early. But at least they said so, rather than just showing up. I've sent people over the road to the pub before when they were an hour early to a large Xmas party in my house. Nothing was ready!
If anything you should come a little late if its not a sit down meal.
But yeah, just say 'no, 5pm at the earliest please as we won't be ready before then but will be extremely busy. And please bring a couple of bottles of xyz'. Here's hoping they get the message!

Yes that is rude IMO, you said from 5 but if she wants to turn up and wait outside for you to get home that's on her!

I couldn’t see this as rude, I assume she’s something before hand so will get there early. I also can’t get my head round you writing you get home at 4.55 and your husband 5 and you don’t mind people coming in the 4 or 5 mins between. It’s all very uptight.

if no one’s in just say sorry. No one’s in, but are you really inviting people to your home at 5 when you won’t get home till 5 mins before hand?

Why would the OP NEED to say she wouldn't be home until 4:55?

She said come FROM 5PM. That could not be any clearer. It's ridiculous to have to justify her day and explain why after 5.

The amount of posters on this thread falling over themselves to explain why instructions wouldn't apply to THEM because they feel special is astonishing.

Lesson learn OP, next time write FROM 5:30 or from 6, so you're ready for the CF 😂

VERY rude and entitled.

If she meant to ASK "would you like me to come at 4:30 to help?", she should have said so.

Of course OP, you can - and have to - tell her not to arrive before 5, but you shouldn't have to. Some people are just so self-centred sadly, you need to be firm.

I’d reply with ‘ok! I’ll find you a job to do!’

Yes, it seems they do. An awful lot of problems come down to lack of communication. I'm guessing she didn't put on the invitation that she wouldn't be in until 4.55pm, just like she didn't put it in her OP. But it's relevant here. Doubtless SIL thought she'd turn up early and help set up.