You can combine the use of Time Bomb and Rewind to place two Time Bombs on a target quickly. Placing the second bomb will detonate the first and stun all nearby enemies.
Time Warp is an effective way to enable allies to finish off enemies, or escape from a losing battle.
Chronoshift is a powerful deterrent to attacking your carries, but casting Chronoshift too early in a fight can cause the enemy to switch targets too soon, making it less effective.
If you're able to match Zilean's speed, it can sometimes be beneficial to wait until his ultimate has faded before landing the killing blow.
Zilean is fragile if a team focuses on him, but otherwise he's very difficult to kill. Commit to killing him as a team.