Make sure your students don't miss the show because of bad timing!
Here's how to control the timing of eclosure. First, record the date each caterpillar forms the chrysalis, and keep that date on a small piece of paper pinned next to each chrysalis. Or you could keep all chrysalids formed on the same date in the same mesh cube container.
Chrysalids emerge in 10-11 days (depending on temperature). Make a list of expected eclosure dates to help plan when you will have emerging butterflies or caterpillars available for showing.
Timing eclosure
If you expect eclosure over a weekend or vacation, you can delay eclosure by placing the chrysalid in the fridge for a day or two. Make sure it's not in a corner where freezing is possible. Each day in the fridge will probably delay eclosure by one day. Keep them in the fridge no longer than 5 days. If more than a day or so, make sure they are misted. I'm not sure what stage in development of the chrysalid is best for the cool period--I'd suggest later is better. You can also delay eclosure by placing the chrysalids in a cool place (like a basement) for a longer period. Cooler by just 5 or 10 degrees F, over the entire chrysalid development would cause a definite (but somewhat unpredictable) delay.
In nature, eclosure happens early in the morning when bright light falls on the chrysalid. This means it's likely the butterfly will emerge before students arrive in class. Here's how to delay eclosure until the students are ready.
As you near the expected eclosure date, check the chrysalids each afternoon before you leave the classroom. For most of its life, the chrysalid is light green in color. But the day before eclosure, the scales of the butterfly's wing begin to take on color. You can see the scales through the transparent skin of the chrysalid. When you can distinctly see orange and black inside the chrysalid, this means it will emerge the following morning. Cover the container (usually a mesh cube) with a dark cloth or black plastic bag. The photo above shows the chrysalid about two hours before eclosure--the colors are more distinct than you'd see the afternoon before.
The next morning, when the students are ready, remove the cloth and place the container where the light is bright. The butterfly will emerge within half an hour, or possibly an hour.
Avoiding deformed wings
An emerging butterfly must have enough space to slowly twist, facing different directions, while pumping blood into and expanding its wings. If the chrysalis is hanging right next to a vertical wall of the container, or too closely confined by milkweed, its wings can't expand and will become deformed.
As soon as the butterfly emerges, it grasps the empty shell of the chrysalid or a nearby object, clinging to it with its claws. If the container is jostled and the butterfly falls to the floor of the container, it will try to climb back up. But if it's inside a plastic bin, it will be unable to climb the slick walls. If it remains on the floor for more than a short time, its wings won't be able to properly expand and will be deformed.
To rescue a fallen butterfly from the floor, offer it a stick or Q-Tip to cling to, then transfer it to a better perch. If you expect eclosure when you are absent, it's best to line the bin's walls with paper towels fixed with tape, so fallen butterflies will be able to climb back up. If wings are deformed, but the butterflies didn't fall or eclose in too little space, then they may have the OE parasite.
Observing eclosure
Don't place the emerging butterfly inside a mesh cube, where they are hard to see. This forces students to look through the mesh, while the light is poor because of shading by the container. Good lighting is always important when working with monarchs!
Instead, pin the chrysalid to a small, bare stick held upright by a jar. Use a small bedside reading light for good illumination of the emerging butterfly.
If you are concerned young students will touch the butterfly--keep in mind that a little touching probably won't harm it. You may be able to control touching by placing the jar in the middle of a table large enough to create separation. Or use masking tape to mark a "no go" zone.
Don't worry that the emerging butterfly will escape. It won't fly for at least 2-3 hours. You can handle it by its wings after they have hardened--4 hours. If you need to move it before 4 hours, let it perch on a Q-Tip or stick.
Feeding
It's fun for students to feed the newly emerged butterflies before releasing them. Use 1 part honey diluted with 9 parts water, soaked on a Q-Tip. Allow their front feet to taste the honey. They probably won't be hungry until the next morning. The outdoor temperature for release should be at least 50 F on a sunny day or 60 F on a cloudy day. Seventy degrees is better.
Link to how to see the chrysalis emerge from the "J."