I don't know what the season is for you. Where i live people are just planting crops outdoors. The plants would be vegging right now and as the daylight gets closer to 12 hours and the nights longer there crops will start flowering. So where you live if the days are getting shorter and the nights longer I believe they will make it to full maturity.
I remember reading in Georges grow bible that some growers start the plants indoors and move them outdoors to finish flowering but this will only work if the days are getting shorter or are at least close to 12/12.

As for determining witch plants you want to keep there is a few ways of doing it. The way I would do it is take clones of all of them and after sexing keep the ones you want.
You can also flower them and as soon as they show sex take a clone of the ones you want. It will not be so far into flowering that it would make much a difference. Just don't rape the plants to bad. Could freak them out. Best take some clones now. Some people switch to 12/12 sex then revert back to veg.
That sounds time consuming.
Best take some clones now and get some practice doing so. :thumbsup: