I raised Black Swallowtails last summer and I happened to have multiple life stages at the same time:

Here is a link that might be useful: Metamorphosis

The article presents itself as an explanation of metamorphosis as it pertains to butterflies. It really should have picked a butterfly, like the monarch, and said this is how the monarch works. Not all butterfly cats do five "regular moults." Some do more. Some do less. Same goes for that "week or two" that butterflies spend in the chrysalis.

The imaginal discs discussion has a flaw. Not all the discs wait for the pupal phase to start developing. For example, the wings start developing within the caterpillar. This is why you can make out the wings on a chrysalis right after pupation.