I've been live-blogging the event on twitter today and here it is! Opened approx. at 5 PM and should stay open for a couple of hours. The sun is already gone from the windowsill but I tried to do my best with the photo.
Good thing you can usually tell in the morning if the flower bud will pop in the evening. This way you can make arrangements like cancel all your appointments. ;) Still, it's only one flower for now with seven more to come. Amazing for such a tiny plant to find so much strength for it.