Chris, to be safe, wait until the pup is about 6" or more before cutting, cut down along the base below the soil. Grass pups are extremely slow growing once detached from the parent. (I've seen concrete grow faster!) In fact, it's often wiser to just buy another small plant than to wait for growth. With my Alcanterias I keep one offset attached to the base of the mother and let it grow naturally from the base. These pups are much faster and sturdier.