O.k. so I'm not a newbie but not advanced either. Tryin!
Anyway....how do you determine the best day to crack open the flask?
I recently bought (my first) two flasks on eBay. One the grower opened and mailed in a plastic baggie still in the agar. The other is zygopetalum mackyii and is still in a sealed baby food jar. The plants are roughly 3/4 to an inch tall but this growers feedback indicates other people have thought flasks received from him weren't quite compot ready. How does one make the decision that, "Today is the day!" What should I look for? Can you wait too long?
You can let the seedlings grow more in the flask (I also saw that guy on ebay with small seedlings), if there isn't growing any mold or something like that. If they are intact, not jumbled around, they can stay quite long there. Be careful: if you will see the agar is getting smaller compot those seedlings, it means that the agar is out of nutritios stuff.
Basically if the jar isn't a jumbled mess, you can leave the seedlings in until they hit the top of the bottle or when the agar starts to go bad. If there is mold or contamination of any sort, take them out asap. It makes a big difference to get the plants as big as possible in the bottle.
Also, in my experience, spring or late spring is a good time to plant your flasks with growing daylight hours and warmer temperatures.