Why do people feel ok to extend their stay / outstay their welcome? And how to handle it .

I never, ever let other people do this or similar to myself or my space.
Ever.
Have zero problems.
Relatives, I'd rather go no contact.
And parents - moved away to another country, at 24.
Why should I force myself to get on with/like people I haven't chosen?

Absolutely this. It's your husbands role to host if it's his relatives.

I don't have anyone in my house longer than an hour, that's plenty.

Haha, like his style. My late FIL, when he thought dinner guests had stayed too late into the evening, would go and get their coats out of the hall cupboard, hand them out and announce jovially "well you'll be off then". Then beckon them to stand and march them purposefully to the front door.

I need to Be More FIL.

I dont know what kind of people visit and then ask to stay longer and putting obstacles on your way . They must know that you are reluctant. If in laws get your DH to deal with them , if friends then both be on the same page . They can't be nice friends if they force themselves on people .

Oh god, I feel tense just reading this. I would absolutely hate it. Love having visitors but I also love having my house back once they leave. There's always chores to sort and I need some quiet vegging time in my own company.

I've had guests in the past like this (not quite as bad admittedly) and it really put me off their visits. One family didn't just outstay their welcome, they were also quite hard work, demanding and messy but didn't lift a finger. I think part of it was that they just didn't understand the effort that goes into hosting. They lived quite near my parents so we always stayed with my folks if we travelled to see them. I think they might have "got it" if they hosted themselves. I phased out their overnight visits. No regrets although it meant we saw them a lot less.

Another family friend who I love very much was am absolute horror for overstaying (daytime visits only luckily). We'd agree to meet up and I'd ask if she wanted to come for lunch or go out for lunch and it would always be "oh noooo, I'm much too busy, I'll just pop in for an hour for a coffee". But then an hour would pass, two hours, three hours and she would still be there and I'd be thinking bloody hell I've had no lunch and now I need to collect youngest from school and my whole day off has just disappeared! A couple of times I had to get up, put my coat on and leave my own house after several hints and she looked really hurt and offended. So confusing given that she was always so insistent she could only spare me an hour so that was what I had planned for. And a real shame because I like her a lot but started to dread her visits. She's moved away now.

My dad always says, as soon as guests arrive, “nice to see you, when are you going home?” He does it with humour but does the job of laying out an end time!

This happens to me too. It’s exhausting and I’ve just stopped having visitors at all because the impact is too big.

It’s annoying and I wouldn’t like it at all but just wondering why a few previous posters are automatically assuming it’s the in laws 🙄

Weekend is too vague. Say Sunday after lunch - if they start pushing back just say ‘no sorry that doesn’t work for us’ on repeat. They ARE inconveniencing you, and it’s NOT an inconvenience for them, just a preference. If you put the expectation that they will be leaving after lunch then you can ask them to strip the beds in the morning so you can get the wash on right away so you don’t have to do it during the working week.
Then after the lunch, you stand up, say lovely having you but must get things done now are you all packed up? If they sit there saying ‘oh we’d like to relax a bit’, say ‘no sorry I really need to get on and we agreed Sunday after lunch, do you need help getting your bags to the car’? Stand there looking at them expecting them to shift. You DH can also chine in and say ‘I’ll get your bags’. If they say they won’t be in the way repeat ‘no, sorry, that doesn’t work for us’.

I don’t have this problem. Before anyone comes to stay I always discuss with them when they will be arriving and leaving.

I find this really annoying too. I found that I had to say “I prefer to know what dates and times guests are coming and going” rather than giving specific reasons as these were always met with a counter-suggestion.

Sometimes I want the freedom to put my pjs on in the afternoon, eat DC leftover beige food for tea and doom scroll for a while in front of the TV without having to be guest-ready, even if they are my parents.

My MIL is abit like this. So when it matters (because usually it doesn’t). I don’t just invite for the weekend I specify days.

If it’s your inlaws I’d just disappear the minute they arrive and not return until they’ve gone and make it your OH’s problem.

If it’s your own family I’d have no issue telling them that they can’t stay anymore as they stay too long.

Stop enabling it all.

I told my friend Phoebe, who is a masseuse, that she can see her clients here starting at 11 am, so you will need to leave at 10.30, because she'll be working here all day. I will be leaving then anyway as I have an appointment.
Or something similar, of you don't feel comfortable politely saying you just prefer your own space.

I learnt that being specific was the answer after the time when DH's parents said they would arrive "before lunch" and they turned up at 8am ...

Don't say "the weekend" or "for Christmas" - they are too open for interpretation.
Say explicitly that you can't host them for more than 1/2/ whatever nights and what time will they be leaving on Sunday? That means about half an hour before this time you can say "oh, you'll be going soon, have you checked you've got everything?" and start persuading them towards the door.
If they ask to stay longer, and you're not happy for them to do so, then say so!

That said, if the reason for not wanting a longer visit is expense, as well as inconvenience, you could always ask them to contribute?

Oh dear, in which case the only thing to do is say:

”it’s been lovely to see you, let me get your coats”

It’s hard but they are being incredibly rude so they’ve brought it on themselves.

I would also make it much less comfortable for them to stay: arrange to “run out” of coffee/tea/milk, bread etc

You need to start being really specific: “you are invited until “11am on Sunday” (or whenever suits you)

If it helps you maintain the boundary arrange (or invent) something you have to do which necessitates you leaving the hose at thst time so that they have to go then.

do None of you work?

was the visit them sitting around the house? Did you organise trips / activities? Did you just have enough food in?

id need to know number of nights and meals they were staying for upfront. And I’d be planning for that. Ie let’s do a Sunday roast mid afternoon in plenty of time for you to get home before dark. Or let’s do Monday brunch here then you’re already on your route home.

Thankfully I have never met anyone who would do this. What is wrong with them.

This. They are taking liberties and don't give a shit about your boundaries @Boomboomi , I'd not be giving a shit about offending them.

You have to be really specific and say what is convenient for you. What would happen if you’d said no?