Took a look at the blooming chart and these seem to be the latest according to that chart:

John L. Crenshaw  (39 days)

Golden Dawn (36 days)

Charles McKellip (32 days)

Red Satin (25 days)

Polly Sharp (25)

Fantastic (25)

Avalon (25) (fertile)

The problem is that  I  can´t find any of them, except for Red Satin, in Europe. I found seeds from Polly Sharp on the seed list from the American Peony Society though. I´m not a member unfortunately so I can´t search their member area for entries about these varieties. 🙁