Perhaps I have answered my own question.
Yesterday, Sept. 2, we had a female laying eggs all over our yard. That has to be the latest we've had eggs in the five years we've been rearing monarchs. The weather last week was fantastic, sunny and in the 80s, and the forecast looks the same for this week. So perhaps the migrants will catch a break after all that rain. Of course, the eggs we just took in (almost 20) will have to hurry at the beginning of October to stay ahead of the cool weather. But I tagged wild monarchs into October last year, too.