Placing Time Bomb on allied initiators such as Malphite and Amumu as they are about to initiate on multiple enemies is a good way to help rack up burst damage. Using Time Bombs on Evelynn, Shaco, Twitch can lead to a heavy unexpected nuke to the enemy team, thanks to these three characters' ability to stealth.
Placing a Time Bomb on an enemy Malzahar's pet 20pxVoidling will cause it to follow him when he runs away. This is great placment for a no-escape insta kill at low HP.
Placing a Time Bomb on an enemy as they teleport may also get you a kill as they will most likely be teleporting to a fight.
You can combine the use of Time Bomb and Rewind to place two Time Bombs on a target quickly. As this causes the first bomb to instantly explode, this is Zilean's main damage combo. This can be very effective for farming and pushing. This combo costs a lot of mana, so you may not want to use it for harassing.
This strategy has an effect on an enemy Zilean's bombs because planting your own bombs on debuffed allies will detonate the enemy bombs.
With minor cooldown reduction and Rewind, you can keep higher ranks of Time Warp on yourself permanently barring mana costs. Use this to quickly get to teamfights to help, or lanes to defend/push.
Repeated usage of Rewind can help to drastically reduce the cooldown of Chrono Shift at the cost of mana.
Using Time Bomb and Rewind can become a reliable farming strategy with higher ranks invested in them. Place one on a caster minion, then quickly place another. The bomb should have done enough damage to leave the caster minion at low health. Land an auto attack on it to set the bomb off sooner.
Time Warp is an effective way to enable allies/yourself to finish off enemies, or escape from a losing battle. By using Rewind, Zilean can slow or boost an enemy or ally twice allowing an easy kill or escape.
Use Chrono Shift strategically for maximum effect. It can prolong the life span of yourself or a team member.
You can bait low enemies to your tower by saving your Chrono Shift till the last second to bait enemies into committing to kill you or die.
Since all of Zilean's abilities are very mana-heavy, you might find yourself quickly running out of mana in the early stages of the game. To aid this, purchase Tear of the Goddess for decent mana regeneration and for early harassment, which can be later upgraded into an Archangel's Staff. This is especially useful if one is also building other items providing mana like Frozen Heart or Rod of Ages. For support builds, this leaves more room for other items, as this is essentialy the only offensive item a support Zilean would need.
By purchasing Guardian Angel and using his ultimate, he can be a great time consumer to the opposing team, which allows the ally team to know how to approach an ambush while you are reviving.
Though, keep in mind that Guardian Angel's passive will always proc after Chrono Shift's active, and generally will ressurect you with a much lower amount of health than your ultimate.
Cooldown reduction is doubly effective on Zilean, since in addition to decreasing the cooldowns of his abilities it decreases the cooldown of Rewind allowing it to be used more often to decrease the cooldowns on your abilities even further. You can use Chrono Shift every 28 seconds with maximum cooldown reduction and continual activation of Rewind.
Zilean's early harassment power can be mitigated by sending a tanky or healing champion to lane against him. You are more likely to win a battle of attrition due to his high early mana costs.
When caught by 基兰的Time Bomb, you can force him to push the lane by intentionally damaging your minions with the explosion.
Remember to stay away from your allies when he uses his Time Bomb on you so you won't intentionally damage your allies.
Ideally you should attempt to take Zilean down quickly with enough burst power to prevent him from making use of Chrono Shift. If this proves impossible, consider that you may need to focus on which of Zilean's allies you can kill the fastest over which one is dealing the most damage.
Zilean's mobility with Time Warp makes it difficult to finish him off without a well orchestrated ambush, but he has low natural defenses. He makes a good target for assassins.
Time Warp is one of the strongest and longest lasting movement speed reduction abilities in the game. The duration reduction from Mercury's Treads is noticable at all levels.
Zilean cannot usually afford to increase his ability damage in the late game and his utility is less dependent on his item build. Attempting to kill Zilean during the laning phase should be a very low priority compared to farming minions.