I'm not quite sure whether this is still right for 'Pleione Spring 2010' as summer has already begun some time ago.
Pleione Berapi 'Purple Sandpiper' did wait very long before it decided to flower this year. I got the bulb early this year from Ian Butterfield and potted it with most of the other bulbs which already flowered. This one just sat there and did not much so far. I guess it is the latest as Pleione saxicola as the earliest of the autumn-flowering ones might start in september.