By sheer luck I got to see it turn from caterpillar to chrysalis. After a quiet period of about a day in the "J" formation, where the caterpillar hangs from its chosen spot (attached to the screening over the container where it spent its final days as a caterpillar) looking like a J, there was some vigorous wiggling, then the skin burst, and rolled up to reveal the chrysalis beneath. The skin soon dropped off--movement ceased, and within a few hours the gold necklace and spots appeared on the chyrsalis. That was the morning of July 25. On the morning of August 5 the chrysalis was transparent and the butterfly within was clearly visible. Then, when my back was turned, the butterfly emerged.
As soon as I noticed I took the container outside and watched the butterfly pump up its wings for a while. Then took the screen off and hung it up on the patio so it could rest relatively safely, and leave at will.
The whole process, from eclosing to flying free took about two hours. It spent the entire time preparing for flight on the screen, first clinging on right by (or on) the shell of the chrysalis, then later walking about a bit. I missed the takeoff, saw a Monarch flitting about the garden by the patio, then noticed that my new butterfly was gone. It was a great relief to me that it all worked out--I'm pretty ambivalent about taking critters out of the wild, being a let-nature-take-its-course kind of nature watcher, but this has been very interesting. I just have two more. One formed a chrysalis on Aug 2, and the other is sitting in a "J" as I write.