To be a bit annoyed my trip has been hijacked?

If he's too young to be getting the train confidently alone, I doubt they're at an age where they'll be lasting partners.

As the parent of adult kids, don't.
Matter of fact to DS.
" I had already planned the day. I was happy for you to come, and your gf too. I am not changing the entire day to suit you.
I want to go for a day out, not a couple of hours. That doesn't suit you. I am not being difficult or awkward. Just being clear.

The cheek of your son deciding that going later will be enough time. It's not his bloody decision.

This is ridiculous. So what if shes working Friday night - shes young, a late night followed by an early start arent going to kill her. This is a case of FIFO - fit in or fuck off. You have a great day planned, if she wants to join in shes welcome but must make the effort

Keep to your original plans - they have to fit in with you, and if that means getting up early, that’s what they have to do

The compromise is that she gets up and goes at the time that is planned. Assuming she's fairly healthy that shouldn't be an issue?

Is there not a train between the 2?

I think you need to tell DS that you are sticking to your original plan and that if it doesn't suit him or his gf, they can give it a miss and you all can arrange something for another time.
Being ND, and being in a family full of ND people, I do get how overwhelming public transport can be. My offer would be that, if they wanted to meet you there, you will write out very detailed instructions on how they can book and pay for tickets, train times, changes, and platforms etc. But you will need to encourage DS to start working towards building his confidence on trains etc. There will come a time when he will need to use it, but will have to rely solely on himself.

You don't believe your son and his gf would be confident enough to make their own way there? Unless they're under about 15 or have SEN I don't see why they'd struggle to do it?

Surely you could meet them at the venue after you've wandered around for a couple of hours alone?

I am glad you are going without them, OP, they were very cheeky to hijack your day out like that and I wouldn't fancy being a third wheel either. Draw your boundaries now. My DD dated a lad in school she ended up going out with for six years and we were far too easy going in the beginning. It got to the stage where he would turn up to everything we were doing, on the assumption he was invited and it was also assumed we would pay for everything, even when they left school and started working. Because she didn't split up with him, we felt too awkward to redraw boundaries as it would have come across as a rejection of him. She was planning on marrying him so we didn't want to cause any resentment. It was our own stupid faults, but never again!

Nice that they wanted to join you. I get you say DS isn’t confident travelling independently , however he is a young adult and needs to learn how to get about , if he is with his gf then that’s a great opportunity to develop confidence and skill.

I would go when you had planned and tell them to make their own way and call you when they arrive. If they don’t turn up you will still have the day you originally planned on your own, if they turn up then you can have a couple of hours all together.

Can they meet you there maybe they can get some sort of discounted duo tickets?

It's fine for them to join you, but not for them to dictate a big change to your plans.

Go early and let them join you later. Surely a young adult can manage a train journey, even with changes? My 15yo could manage that fine, and there'll be two of them.

I was creating stress for no reason and that it would be enough time

its your day out, its not for others to decide if its enough time - that is incredibly entitled and dismissive of you. They invited themselves, you welcome them and then they pull this....

@HardyPlumEagle As everyone else has said - do NOT agree to wait until later. You have to say that it doesn't suit you to wait. You wanted to go all day, not just for a couple of hours. ND or not, it is very unreasonable for them to expect you to wait for them. Just TELL them no.

If he's old enough to have a GF he should be able to arrange his own trip. Go when you planned they probably won't come anyway .

I would say: I planned this trip and I was really looking forward to spending the whole day there. Two hours may be enough for you but it's not for me. So I'll be sticking to my plans and if you want to come along that's great but if it doesn't suit you, you can make your own arrangements. And I don't appreciate being called a creator of stress . I am entitled to do things I want to do with my time.

Your trip has not been hijacked by your son, it has been hijacked by you. Just carry on with your original plan. If this doesn't fit in with them, too bad!

Absolutely this. If the GF can’t/doesn’t want to get up in time, tough.

Just go as planned, leave it up to them if they want to come, their tickets and train fares are up to them, it sounds like they are 17/18 if not older so there is no need to pay for either of them.

this.

I think he needs an explanation that if him and his gf want things then they need to start paying for them and sorting themselves out. They can’t go demanding that you do things for them and change your original plans and then when you push back saying you are causing them stress.

ND or NT That is controlling. If he feels able to demand things and gaslight you into thinking you are the problem I would be looking at how bad his ND is.

How dare he say that to you

I would be going nuclear on him.

Young adult son has a girlfriend but can’t navigate a train?

No way OP!!

This is your day out and you wanted to spend the entire day there for a reason.
What a waste of money just going for half the day.

Tell DS that you’ll be going for the full day and that you’ll do it again another time even him and his gf can join.

You're not creating any stress. You have a plan you are happy with it. They want to change it.

If they want ro come with you they come with you.

You arent creating stress. You have a plan, ds is welcome to join as planned. His girlfriend also welcome. They can come at the planned time or meet you there later. You could not be more relaxed about the arrangements. (Ds wont be getting train alone if he is with gf.)