I WAH about 20 hours a week, so my situation is a little different. We found a regular sitter/nanny through a local service called Mother's Helpers, who comes and watches the girls during that time.
She's fantastic and although she didn't have specific experience with kids on the spectrum, she did work for another family with a child with medical SN. My girls adore her and I really feel like we lucked out. She's in her early 20s, and couldn't find a job in her chosen field after college, so she's doing childcare instead.
I do drop-offs and she picks DD1 up from school, driving our car. I thought I'd have a very hard time with someone else driving my kids around, but when you find a trustworthy person it's easier than I thought. The other parents at preschool have asked if she's a relative and told me that she's very good with the girls, which is nice to hear -- I know she's just as good with them when I'm not around.
We've also had our Floortime therapist come and do a couple of sessions with her to help her know more about autism and about DD1's habits/quirks in particular.
The nice thing about the Mother's Helpers service is that although we have set hours, we can also call her or the service any time to ask for coverage if, say, we want a night out. We may even ask our sitter if she's willing to do a weekend day sometime so that we could go skiing -- which we'd be completely comfortable with, and wouldn't be an option otherwise b/c we have no family in the area.