AIBU to think 8.45pm is too early to expect quiet?

Completely unreasonable! I have hardly had tea by that time, let alone be silent!

Depends how loud you are being. Having the TV or music on at a normal volume or general chatter between people is fine and hearing it through the walls is just a part of having attached neighbours. That said, I think playing loud music or having raucous parties where people are shouting or singing at the top of their voice etc isn’t ever really reasonable in an attached house, nobody wants to hear that at any time so if the neighbours have asked you to be quiet I’d honour it.

Yanbu at all. It's ridiculous of them to impose like that.
Yabvvvu to say you brought your house though. You can't bring a house anywhere!

No OP didn't say anything about what the noise actually is or how loud it is. She just said they are socialising.

A group of teenagers socialising could be anything from 3 or 4 quietly chatting, to 11 or 12 listening to loud bass music/ drinking/ getting a bit out of control and boisterous.

There's a pretty big difference.

Also, most parents of 4 month old babies know all about white noise.

Yes, my suggestions will not help if its a drum and bass fest next door. I think the poster said they were not overly noisy so hopefully its sufficient.

What were you doing?

This so the question isn't it? If they are asking for silence they are being unreasonable, if they're asking that 10 teenagers aren't playing aloud music in the garden then they're very reasonable. Op needs to return and explain

In the 80s my mum had 5 of us in a 3 bed terrace, next door d neighbours had 5 and their eldest as the same age as my youngest sister. There was lots of little kid noise nextdoor and lots of silly teenage noise in our house. My mum and my neighbour had the same age difference as me and the neighbour. They got on great. My mum took the babies in when my neighbour had a doctor's appt, I remember her just wheeling a double pram with a sleeping baby and toddler into our living room behind the sofa while I was studying for GCSEs. My neighbour kept an eye none of us burnt the house down the odd time both my parents were out.

When did people get so intolerant and expect silence but also expect to make noise indiscriminately?

What are your kids doing to make noticable noise? At 14 and 16 I'd expect them to be past the crashing about stage and able to understand normal conversation volume when they've pals round. I'd expect them to know how to keep music or tv at a reasonable level and I wouldn't mind asking them to stock headphones on past 8.45. what is the noise that's problematics?

my neighbour used to bang on the wall at 8.30
they moved thankfully!

Depends what noise they are dealing with though.

If it's just chatting in the garden then yes, sure, but a bit of white noise and a fan won't drown out loud music coming from next door.

What exactly is the noise, OP?

If it's loud music every day then YABU. I don't see why that can't be turned down or off to support a neighbour with a small baby.

Evening music is fine as an occasional thing, but not every night.

If it's just teenagers chatting and socialising then YANBU. Your kids need to be able to live their lives, too.

I think 9:30 to 10 o'clock is polite and very reasonable.

I wouldn't even be quiet for my own kids at 8:45 on a school day!
10pm to 9am, or 10pm to 10am on a Sunday is fine.

Id suggest they try strategies for their baby such as white noise - an air purifier in the room or a fan would be good in the heat or a radio or cd of background soothing music (harp or soft piano soothing music). this would all drown out street noises. If the baby is unsettled (which many young babies are) then the answer isnt to expect the world outside to be quiet from a certain time, but to look for solutions. Their brains are probably fried from fatigue so maybe suggest some of these strategies to them.

The baby is 4 months. There's a thing called the 4 month sleep regression. It will make no difference what time your teens are quiet, their baby will still have crappy sleep for the next 1-2 months.

How did they let you know they were unhappy about the noise. Did they catch you off guard, as you could have told them that you used to use background noise of a radio or white noise when you had your babies, so they would not hear external noise.
Its bad enough that you would have to be quiet for your own kids when they were small, never mind the next door neighbours, years later. I would not be happy telling my own grown up kids to be quiet because someone else has a baby (in another house)

Have they tried white noise in their baby’s room, to mask outdoor sounds?

Alexa volume 10 LOL

My neighbours let their teenager hit a ball against the concrete wall until sometimes 10:30 almost 11pm at night. My toddler’s bedroom window is overlooking the garden. This disrupted her bedtime as we moved it from 7:30pm to 8:30pm, to 9pm
which meant it was very difficult for her to wake up the next morning. We ended up taking her into our room to fall asleep and then moving her to her bed around 11pm. The knock on effect was that she woke up at night in a different bed to where she fell asleep and came looking for whoever put her to bed! Absolute nightmare for us as I have to get up at 5:30am! I’m house hunting at the moment, and will hopefully move once we can afford to. I have two older kids and I would always teach them to bed considerate of their neighbours.

Depends on the noise and type.

This! Let them know this in a nice way. We put the radio on while ours was little on purpose and he even sleeps through the odd shouty argument, the dog barking its head off and the doorbell, and obvs the telly and everything. So glad we didn’t tiptoe round him!

I have teens and make hen pipe down inside at 10pm
and outside at 9pm.

Just kid on you are all in bed for 8pm and it must be another neighbour making all the noise? 🤣.

Is it their first child? Are they following some regime that states baby should be left to sleep and needs a strict routine? No - babies haven't read the rules and it probably doesn't appreciate being left alone to sleep. Plus of course, currently it's very hot, and possibly stuffy in its bedroom. Maybe it has colic too. You sound as though you are a thoughtful neighbour, so they need to sort themselves out, and legally you are entitled to make normal noise, until at least 11.00 pm.

At no point does OP say 8.45pm would be fine. The whole point of the thread is that 8.45pm is not reasonable or fine to expect neighbours to be quiet.
I see someone else answered you the same way I did. I have no idea what your point is…

That wasn't my point. She said 8:45pm would be fine but 9pm not - it's 15 minutes. Regardless of whether it's term times, holidays, or the seventh Sunday after Michaelmas.