In three days they had almost tripled in size - almost 3/8".
The larvae will continue to develop for about another week before turning into a pupa (chrysalis).
I haven't seen any monarchs in the yard, much less laying any eggs, but I continue to inspect the leaves for eggs every day or so.
Last year I only got two through to adulthood - my lowest count in all the years I've done this. I'm thrilled to have 8 larvae already.