It depends for me but I am not sure what the pattern is. Let's see.
I get extremely anxious and depressed when I graduate a school/end a trainee job and am forced to look for a new job/school, find offers, sent CVs. I will get a lot of meltdowns and shutdowns during that periods.
But I will also get excited when all is set (nice job offer found, CV sent, they invited me for an job interview) - I will happily imagine myself working there and go to the interview quite happy. Stressed yes - but excited too.
Then the interview is over and my repeatable meltdowns and shutdowns intensify while I am waiting for an answer(because I don't know if they hired me or not and I can't know when the phone is going to call so I can't plan anything, I can't even go to restroom because they might call).
But when I actually start a new school/job I adjust easily. Unless the job environment doesn't fit me and people bully me from the start(it happened in my previous test job).
I am the same with fun events. For example going to vacation or a trip. The organizing part freaks me out and my meltdowns/shutdowns intensify before it's all set but then ... I just go there and adjust so easily as if I always lived there. I even sort of forget how my house looks like after 2 nights in a rented room. I do remember but it feels as if I was remembering something I left 10 years ago, not 3 days ago.
There are also the sudden changes during the day, "We are leaving in 10 mins". My reaction to those seems to depend on what I was doing, where we are going and if I am forced to go if I don't like it and If I have enough time to prepare. I will generally be angry if they wake me up to tell me this (if you want to leave at 9AM let me know the evening before so I go to bed early and get enough sleep!), if I am busy("Not 10 mins, 20!") and if they hurry me("We are waiting, why so slow?") especially if they lie about the time ("It wasn't 10 mins, I am already waiting half of hour for you!") because "Time flows differently depending what side of restroom door you are"(= the one who is waiting always feels more time passed than reality)
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But later in the day, especially about the time mom gets back home from work I sort of can't wait for them to say something like this because I am bored at home and I want a change of pace. When I hear "We are going to a shop/grandma/neighbor city/train station/whatever." I will answer "Me too!" and get ready as fast as I can(It could be as fast as picking my bag up and going to restroom or as long as "Just give me 15 mins, I need to finish here").
And I can't say I really have a routine to follow. It could be because my house environment is unorganized. I had to adapt or I couldn't survive.
Especially my mom, which I share the trait with - I just "have to" reorganise my room every a few months and I like changing stuff in other rooms too.
My dad (probably in the spectrum but not diagnosed) hates that one. He yells at us when we change anything in the house.
Dad doesn't like change but he is the one forcing us to be adaptable because he never communicates what he plans for(he does, but we have hard time guessing if he is joking or really means it because his body language fails) and expects everyone to follow the plan. So I had to learn to make my decisions fast and improvise.