By the end of May? Um. Don't think you do. Usually it's about a year from planting a leaf to flowering of the split-up babies. I've had one baby violet bloom after it grew two leaves (!) but that was a mutie and never grew any more leaves. They'll need to be about 5-6" across the leaf whorl (if normal plants, not miniatures) and have bright light to trigger flowering. South facing in winter and E or W (not direct sun) in summer. And as close to the window as you can during the day (but don't leave between curtains and windowsill at night as the temp drop can kill them).
Let them be for a few months yet, and you'll have a lovely display by Christmas. A plant diameter of 9cm is too small really. I'm in a similar position with several babies, and am hoping they'll be ready for then.
moonbells