Yes I planted some potted peonies a couple of years ago and the are doing just fine,although fall is the best time because it gives the feeder roots time to grow.It may not look so good for a while and the foliage may wilt but just keep it watered so the roots have a chance to grow.I always try and water at the base or around the edges and not on the foliage to reduce the chance of blight.Good luck I'm sure next year it will come up just fine,also don't plant more than two inches below the ground and mound or mulch the first winter to prevent frost from pushing it up.

I think it should be fine. It was potted already. So transferring it to inground should not be that much of a problem. As said above, don't plant deeper than it was in the pot.

I think you did just fine planting it as and when you did. My only concern would be the different exposure coming from the growers greenhouse into the full sun of your garden. If that were to be a problem you would know it within the first few days. I recently bought a very large, very full, VERY CHEAP, peony from Costco. When I was finely able to get it out of the pot the soil was as dry and hard and fully packed with roots as I have ever seen. With the plant in bloom and so packed with stems I was afraid to do anything drastic to the roots. I just planted as it was in my peony bed and soaked it well. The next day it was wilted and I soaked it again. The weather was cool and not much sun. It took about two weeks of babying to get this peony to stop the periodic wilting. This fall when the plant goes dormant I will dig it up and break up the root ball, divide it,if called for. I guess the lesson is a plant may have a good reason, for being CHEAP. Al