I leave the seedlings in the flask as long as I can, when they look relatively large and healthy, that's when I deflask.
You have done the right thing at the right time. If you get a few starting to turn yellow deflask straight away. I have kept some of my flasks up to 3 weeks prior to deflasking just to get them up to size.
You can expect at least 50% success rate with the seedlings, that's why there are so many in a flask. Keep the big buggers and get rid of the little tackers.
My first foreray into flasks was the Balinese seedlings, I have learnt a lot since October last year when I got them.
I now keep the bigger healthy looking plants and discard the runts, and in the long run it pays dividends, plus you don't have hundreds of seedlings to care for., Mine have taken up space of plants I would love to have in my collection.
But, it was a learning curve I needed to experience and as long as I have at least 4 from each species, I'll be happy. At present I am well above that figure, but they are a real pain in the you know what to have to look after so many.
Just my experiences.