Is it too late?

I live in Southern Michigan. I found a caterpillar and brought it inside with some milkweed to eat. As I started looking for more milkweed plants, I found 6 more caterpillars of various sizes and also brought them in. Will it be too cold to release them if they do turn to Monarchs? Also, since I have no idea how many times they have shed their skin, about how big do the caterpillars get before the process starts. We are eagerly awaiting some kind of change.

Thanks,
Sandy

Karen says:
Sandy, the caterpillars you have found are all ones that will migrate to Mexico. If it is cold when you release them, they will just wait until the weather warms to start their migration.

The caterpillars will molt 5 times (including the last time when the chrysalis is revealed). This will take 10-14 days. Also, check out more information on the monarch caterpillar.