Last year, I found the first egg April 28. That was a little earlier than usual: In 2008, the first was 5/7. In 2006, first egg 5/4. But I was not prepared for the numbers. I expect to have to use the whole dining room table during the Aug-Sept craziness, but not in May. I'd clear a small place on the table, put one cage out. Go to the garden, find more eggs and cats. Get another cage out. Forage for milkweed, bring home strays. By the end of May, 32 butterflies had eclosed.
Then, the lull. Just 2 butterflies in June and July.
The real wave started around Aug 8, as it always does. Our house (just an average suburban house with 2 patches of A. tuberosa) raised just over 100 more, with the last eclosing the first week of October.