When I've agreed to be somewhere, I feel I have to be there on time and can't cry off or be late except for emergencies.
My absolute nightmare is long-distance appointments. I have to catch a ferry next week and my ADHD wants to get there at the very last minute because there will be so much hanging around after registering arrival, but my autism wants me to leave plenty of time for the journey in case something goes wrong, so I'm anxious on the journey for fear something will.
How do you cope?
Why is my time less valuable than thiers?
Alas, my experience of the NHS is that patients' time is considered irrelevant.
Is there anyone at the ferry terminal that you can sit?
It's like an airport with everything airside, but you have to sit around in a bare room for 20 minutes or so until called to go through security. On the "seaside" (just made that up for the airside equivalent) there's a cafe, but no indication of when foot passengers will be called to the bus, which is always last minute as they board vehicles first. Maybe this time, I could try asking for some indication of when these things might happen.
I need to create some checklists
Oh, yes! I've kept checlists for years. Without it, I'd be even more of a wreck. 
I have become much more relaxed about appointments with age and while my autism is always pushing in the background to be there on time I have found that there are few situations in the real world where a delay of 10-20 mins is really much of an issue.
For situations where I need to be on time then I aim to arrive 15 mins earlier, or if there is a higher risk of delay (eg using trains or driving to a different city) then I increase the amount of time in advance to arrive accordingly.
Preparation is the key - not only to know how to get there (Google maps and street view make identifying the building so much easier) but to have alternatives if the parking is full, and to have a few contingency items with you.
I always carry a small bottle of water, a set of things like headache tablets, indigestion tablets, chewing gum, something easy to read (eg magazine) to pass time and a pack of tissues in case of allergies.
Pre-load any maps offline on my phone so I am not impacted by lack of mobile phone signal and I am set.
My autism helps me a lot in these situations as I can see the probable issues I will encounter and can work around them.
What experience has taught me is that things can go wrong so when they do then plan a response to avoid the panic response that some people talk about - it leaves you feeling confident and much more likely to get more from the meeting.
When things do go wildly wrong (eg the train network goes offline) then treat it like an adventure and not a disaster. Contact the person you are meeting as soon as you realise and tell them the issue and that you are switching to an alternative plan or are cancelling. If it is on the return leg then treat it like an escape room challenge - a puzzle to solve.
If the worst happens and you are trapped far from home them get a hotel room for the night rather than get into a tizz over it all. I've done this a few times and it allows me time to plan an alternative for the next day, have a good nights sleep and maybe treat myself to a nice meal out.
Where I live now it is quite common to be an hour late due to a mix of terrible traffic and the local culture so this makes expectations much lower for punctuality and gives a more relaxing lifestyle, even if the lack of structure rubs against my autism at times - I always have something to read with me and can chill in a cafe while I wait as my planning normally lets me arrive on time.
I like, actually I need, to be "there" about 5-10 minutes before the "thing". For me it also eliminates the stress/panic of being late. To me it is just good manners and was expected when I was young. I can recall Mum saying "you can go out for the day but you must be back by 4 o'clock, whose got a watch". Us kids could have been up to anything, and sometimes were, but getting back on time was an imperitive.
I always plan journeys in detail to (try and) avoid being late. For me, what "on time" means depends on the context.
For medical appointments, I try to be a few minutes early. But also allow for delays - like having to hunt for a space in a busy car park. For work-type meetings, I was taught to arrive around 5-10 minutes early. For holidays involving flights (not that we've been away for several years), we like to get there really early. But we do use airport lounges, so it's not the same as the general concourse, which I wouldn't like at all.
That being said, I've decided that I need to create some checklists, to help me prepare for different kinds of trips (eg GP, hospital, vet, National Trust place). Because, despite planning journeys carefully, I often still end up in a panicked rush at the last moment, having forgotten to do - or pack - something or other. And so can often still end up being late and feeling stressed. I was trying to resist using yet another coping system, but it's time to just give in and do it!
Is there anyone at the ferry terminal that you can sit? You could take yourself a packed lunch or a book or a puzzle or whatever you like to do. Then you can be early for your appointment without having to actually turn up early.
Grabbing a coffee or meal is a good idea and I might try it for other appointments. Unfortunately, ferry terminals only have vending machines. I'd have to find a car park in the nearest town and that won't work for me as it will add to anxiety.
I absolutely have to be there early. My wife occasionally reminds me of the occasion when I dragged her to Heathrow an hour earlier than necessary for a flight to Glasgow. (OK, part of the reason was that the noise and crowds of central London were pushing me towards a shutdown.)
Forever early for absolutely everything. And incredibly irritated when others are late, why is my time of less value than yours?
I can be sitting in meeting rooms at work for 10 minutes or so until someone else arrives.
It’s a combination of priding myself on never being late for anything, and the anxiety of missing something.
If catching a train I usually get the one before I really needed, and even then get to the train station early. I always factor in far too much time for something to go wrong on the journey.
It drives my wife mad, but she also knows I’ll be a bag on anxiety of we don’t.
I hate having to be somewhere by a particular time, I get really anxious, I think it comes from my Dad who had to be eveywhere early which often meant hanging around drafty train stations for an hour before our train left.
What really disses my grunt is when I have to be on time, but the person I'm suposed to be meeting isn't, like some medical appointments, I get if theres an emergency the doctor might be needed elsewhere, but why is this never acknowleged, why can I not be told and asked if I'm happy to wait or would rather book another appointment. Why is my time less valuable than thiers?
Luckily I rarely have to be anywhere at a particular time anymore, another source of stress removed, yay
I don’t cope. I have a chronic time keeping problem to do with not understanding how long anything takes. I do my best not to arrange anything too firmly if I can’t help it. Long distance travel to a timed appointment is my idea of hell. I would aim to get there early and have a cuppa first.
I am AuDHD too and it's a constant battle. My autism wants to be there at the exact right time and worries about being late. ADHD thinks I've got more time than I do and hates waiting around. I've got it wrong so many times before I also think I overcompensate sometimes and wildly overestimate how long I need and end up stupidly early. One thing I have found helps is make the start time 15 minutes earlier. That start time is my goal and I'll usually miss it and end up being closer to on time. I totally understand the anxiety - so many what ifs for the journey. Is there anything near by you could do? When I've had far away appointments I've aimed to get there early enough to get food first. Say it was a 2 o clock appointment. I'd aim to go to McDonald's first. If I get delayed, the worst case scenario is I go to the appointment hungry and get food after it. I've never had to get a ferry for an appointment though. If they don't run very often, I can see that raises the anxiety.
