New grower

From the research that I've done on my own as well as with my grow so far, the consensus seems to be that you always want to ensure you're transplanting before your root system gets crowded in your pot in order to prevent them from getting root-bound. Some people refer to the leaves of their seedlings and they wait until the leaves start to reach the outer ends of the pots diameter but you still wanna keep the structure of your pot in mind. Other ways you can tell when your seedlings are ready to move on are when the roots actually extend past the drainage holes but I wouldn't wait long after seeing this. Get that baby a new size home! Otherwise, let them do their thing and take over until they are ready. Expect your plants to possibly get droopy after the transplant. Shouldn't take to0 long for them to bounce back as long as soil & environmental conditions are adequate ;) Hope this info helps!

Normally, when the first real leaves start to protrude outside the circumference of the jar or glass it will be time to proceed with the transfer