Yes, a multiturn sundial mechanic is very potent. That is why I tried to make sure this card would only affect at most 2 creatures (the on in the owner's slot and the one in the enemy slot)... is this still too much? I was hoping that by limiting it to a single slot rather than all creatures it would be balanced.
The return mechanic can be altered so that it returns at the end of turn instead. This would give the opponent a 1 turn reprieve every 2nd turn.
Also, if the return mechanic is used, it ends up being a 2 turn sundial, if it is not returned it acts as a 3 turn sundial.