Hi,
My ingame name is Call Me nUc3 and i play LOL since season 3. I main support since season 4 and would like to help other summoners to become a better support.
Here is my first guide so dont be to hard.

Important words to understand the guide :

ADC - Attack Damage Carry
APC - Ability Power Carry
DMG - Dmage
AOE - Area of Effect
hp - health points

+Good Poke Time Bomb
+Good Engage/Disengage Time Warp
+Revive Chronoshift
+low cooldowns Rewind


-Squishy
-No hard CC (Stun, Snare, Knock up)
-No heal
-No Shield

You have to Start with Spellthief's Edge otherwise you won't get as much gold and you will deal less DMG. Also buy the Stealth Ward to get some vision.
Thanks to the Masteries you will have enpugh gold to buy 2 Mana Potion and 2 Health Potion and you will mostly need them.
At the first back you should get Tear of the Goddess or Sightstone because otherwise your mana will be empty very fast. If the jungler is Ganking often you have to buy Sightstone and change your Stealth Ward to Sweeping Lens.
If not buy Tear of the Goddess and start to buy Chalice of Harmony.
It is always good to buy some Mana Potion and Health Potion.
You don't have to buy Boots at your first back because of your Time Warp.
As i mentioined in the notes you should only buy Locket of the Iron Solari if there are 3 AP champions in the enemy team or 2 and one of them is fed.
Rabadon's Deathcapis always good if you are a bit ahead and need some poke you can also buy Mejai's Soulstealer but that is a more risky buy because you need the stacks on it.
If you have to lane agaionst Leona, Thresh, Taric, Zyra, Morgana, Sona, Annie, Karma or Brand you should defenetly buy Mikael's Blessing to clear the CC.
You should buy Boots at you second or third back even if you dont really need the because of your Time Warp some extra speed is always useful and you should upgrade them fast into Sorcerer's Shoes to get the magic penetration.

In the laneing phase you should always do a Time Bomb - Rewind - Time Bomb. If you land this combo the first Time Bomb will explode immedietly and the second will explode after 4 seconds.
You can also use your Rewind to lower the cooldown of Chronoshift and i would highly recommend to do this.
When you reach lvl 18 and 40 % cooldown reduction you will be able to give you speed with Time Warp until your mana is empty if you youse Time Warp - Rewind all the time.

It is always good to have much AP as Zilean but you shouldn't forget to take some defensive Runes.
I would only switch the Glyph of Magic Resist into Glyph of Ability Power when the enemies dont have an AP support.

Zilean is a good Champion for teamwork.
You can speed up yourselve or an other Champion ( Time Warp) or revive them Chronoshift.
I would recommend to save your Chronoshift for the ADC or the APC so they can deal as much DMG as possible. You can also try to use your Chronoshift right before the person dies so they are not going to change the focus and he will be back with almost full hp.
Zilean also got teamfight potential because your Time Bomb is doing AOE DMG and you can slow a enemy down if you want wiht your Time Warp.

I think Zilean is very underrated support.
He can poke poke very good with Time Bomb, speed up someone with his Time Warp and revive anyone in his team with Chronoshift. He dosen't have so much cooldowns thanks to his Rewind.
Zilean is also fun to play if you like to poke your enemy and run across the map with much movement speed.
The only bad thing is that he is very squishy but if you get catched you can use your Chronoshift and run away with your Time Warp.
All in one Zilean is a pretty good support if your team needs some extra AP DMG or the enemy team can burst out your ADC or APC.
Good luck in the Summoners Rift.