Very interesting! I'm in Seattle too. I got my cherimoya seedlings to start, but I'm wondering when they can go outside and when I'd have to take them back in. Right now they are in a sunny window with just four leaves apiece (so they are still baby cherimoyas).
You can move them outside now keep them in the shade away and covered from rain for a few weeks. They dont like wet feet. Then you slowly move them to full sun. I bring mine inside in october.
I wanted to update you! My cherimoya is now about 12 inches tall and thriving. Thank you so much for your advice.