"Tu en auras la moitié, quand il sera là."
I had the same question but then I checked here examples of usage: http://www.linguee.fr/francais-anglais/search?source=auto&query=quand+il+sera+l%E0.
My assumption now is that when you use "when" you already imply a future tense, hence the actual structure is unnecessary.
Now I wonder why it is not the same in French. Doesn't "quando il est là" convey the same meaning?