IME, Helleborus x hybridus will throw the odd bloom at pretty much any time of the year - who knows why! I currently have a selection in at my nursery that are all showing color and many in a bloom cycle that rivals their normal late winter show.

They are pretty tough guys and react to periodic cold spells well. We just experienced our first hard frost with temps into the 20's and while the flowers looked limp and droopy, by midday with temperatures in the high 40's they had perked up and looked great.