Interesting, Cinda.
A gardening friend in Iowa just said to me yesterday that primulas won't grow there.
On the other hand, have read that some primula will grow in the Mid-West, including in Iowa and Indiana (latter, as you indicate).
Obviously though, not all growing conditions in all locations/gardens are the same.
As to 2 or 3 (weeks), I'd say most of our own primulas are in flower just through May;
so perhaps for a month, though the primula flowering is extended into June by the later blooming candelabra-type primulas, including Japanese primulas.
We have hot summers which are also humid.
As to the sun, in our garden, the primulas are shaded by the taller perennials through summer.
Thanks for the advice. I have found that plants that like the cooler climates are not so much about heat tolerance as they are about needing a cold spell. I noticed last year that people in the Midwest were much hotter than me with tempts up near 120°. The highest we got was 102°, I only thought I was dyeing mainly because of the humidity it feels like 120°. The problem here is that the plants do not get a good enough cold spell. Some things won't bloom and other things fizzle out because the dormancy period is not satisfied. 
