One of the benefits of having a yard full of native plants is that you can easily observe the life histories of many insects including butterflies.
Many years ago, while walking through our yard, I spotted a monarch caterpillar hanging upside down from the leaf of a Fireflag (Thalia geniculata). It had already fastened its cremaster to the leaf and was in a "J" position. This position is characteristic of many butterfly species when almost ready to shed the final skin to reveal the chrysalis.
My wife and I ran inside to get our cameras to capture the event. I took a few quick shots (with a film camera then) and set up my tripod in anticipation of getting some really good images of the "change." I knew it would be quite a while before the monarch shed her skin so I went about other business and checked every fifteen minutes or so to monitor the caterpillar's progress and take a few additional photos. It was about 11:30 a.m. when we first saw the caterpillar and by 2:30 p.m., we could see that the outer skin was getting more wrinkled, a sign that it would not be much longer. This is when I made my critical mistake: rather than sitting there for the next three hours, I thought I could leave and just check the status every five minutes or so. I last checked it at 2:45 p.m. with no visible changes. Fortunately my wife was also checking its progress and by 2:50 p.m., the skin was already beginning to split to reveal the newly transformed chrysalis. She had her digital camera set up as well and began snapping photos while screaming to me, "Get out here! It's changing!" Neither of us actually photographed the moments before the skin split to reveal the green chrysalis.
Watch a video of a monarch butterfly emerging from its chrysalis in The Monarch Butterfly: Emerging from Its Chrysalis.