Man you can leave them in there for pretty much as long as you like, just make sure roots don't become tangeled. I don't transplant out of my cloner until I have roots that are at least 8-12 inches long. One time I left one in there until the root mass was as thick as my forearm. So yeah you're golden man. You might want to put them on super weak nutes though like 1ml per liter, but I wouldn't worry about that until the roots hit the bottom of your rez.