Why not just target the old-fashioned way and then retarget with "/targetlasttarget" if you want? That way you wouldn't need a delay. I think you would quickly get dissatisfied with whatever delay you choose because it's either going to be unreliable (a short delay will fail when your ping gets long) or it will add unnecessary delay to your healing process.

Ok here is my idea, I've been at this for a while now and it has all but halted my leveling.
IMO level 13 is too early to be hung up on niceties like this. Get back to leveling! :P