On April 17 one Monarch female came in my yard and laid over 115 eggs on my Butterfly weed plants that are only 4-5" high and most of the plants are just coming up through the soil. I live 10 miles out of Nashville Tn.
Unless you have a good source of milkweed, I'd leave them on the plants. Last year, I left some outside to hatch. It took them three weeks. That gave the milkweed time to grow, too.