Don't use exhaust! I dont think you have enough mana regen either

I don't really see the purpose of Exhaust other than the blinding aspect, since you already have enough speed manipulation. Why not go for Clarity? Also I think the Ignite Mastery Point isn't worth it late game, and you really want to build up gear so you can get kills in that late game. The 10 AP is marginal by then.

Good build though, made me try Zilean :p

time bomb 5 on level 8? should be 9 ;)

One thing that I think you've overlooked is the absolute importance of the Golem Buff to Zil. In mid/late game get it and keep it on you. With the Mana Regen, CD Reduction from the buff and lvl5 Rewind you can keep Time Warp on you 100% of the time. Using with No.2 move boots gives you a permanent 500+ move speed for the duration of the buff. Even if your mana is just decent the buff will keep your mana full as long as all you cast is Rewind and Time Warp. I just played a 2v2(all people) Practice on SR(Yah I know just practice) but by end game I was able to single handedly push ALL 3 LANES.

Slows don't stack and you got 3 of them so...

Actually, I played in lane against almost the same Zilean ( i mean almost with the same build (mostly AP) ), but he was no match for me, since i play with Janna. He changed lanes, cause i was owning him and he did pretty good to win the game for the opposite team. Zilean is really an OP champion, he must be nerfed.... but he is OP only for the ones who can play with him ! The build is good, i'll vote with + ;)