How soon can you take a come from a plant?

in my exp, young plants don't have a high success rate, but as soon as you can take something with which you can bury a node and has a growth tip, there's a chance it lives. Usually there are not a ton of opportunities before a month old anyway, and you'll want to take more than you need. If extra survive, you throw the weakest out. it's win-win. Also, make sure it is in as best condition as possible before taking cuttings. A healthy mom = high success rate. The later into bloom the longer it'll take to root and start to grow. Stick to vege clones if you can.

I assume you mean clone, I would advise to start about the 2nd internode of any branch. as soon as they are the right length that is.