I have been talking about "cohorts" in my posts, but I should explain that I don't mean to say that these correspond with cohorts in the wild. I am using the term cohort to differentiate among the batches of eggs laid in captivity by different females this summer. Here in Ontario Papilio canadensis only has one cohort. According to the Ottawa Field-Naturalists' Club the flight season runs from mid-May and ends in early June. This is definately consistent with what I saw this summer in the field. For comparison, Papilio polyxenes has 2 flight seasons. One starting at the same time as Papilio canadensis (mid-May), ending before the end of June. The second cohort runs from mid-July and finishes at the end of August.
This information came from the "Checklist of the Butterflies of the Ottawa District" compiled by Peter Hall, Ross Layberry, and Don Lafontaine in August 1996. It has the flight seasons of the 80 most common butterflies. Maybe the best $2.00 I ever spent.