Three days after dropping Matirin off on the Andalite homeworld, Leareth finishes the spell, and artifact to cast it, to imitate the morph tether.

He doesn't do this one in morph because he's not sure how long he's going to end up spending in the Void, and it can be harder to keep track of time. As much as he appreciates the Andalite body, he has no desire to end up stuck in it permanently. 

He sits down comfortably, artifact in hand, and anchors one end of the spell on the nothlit rabbit munching celery in its cage in front of him, then leaps into the Void, watching the spell unfold and looking for the reduced existing tether to the remains of the rabbit's normalspace pocket.