How long does it take you to adjust to a different work schedule?

FOREVER.

The last job I had switched me from day shift to night shift over a weekend, and even though I had the weekend to try and adjust my sleep schedule, it still took me over 3 months to finally be able to stay awake during my night shift. I hated it.

A while I'm autistic so messing with my routine is bad for me

21 days as per research

I think that would require someone to be dedicated to their work to make it look like a breeze.