User blog comment:Xyclone010/CCC4: Lustrum - The Time Mage/@comment-3974211-20140708142219

Assuming I've understood it correctly. Time line:
 * 1) First cast generates first empowerment stack, increases the cooldown to 5.5 seconds.
 * 2) Second cast is activated 1.5 seconds early (at 4 seconds) but generates a second stack that increases the cooldown to 7 seconds.
 * 3) Third cast is activated 1.5 seconds early (at 5.5 seconds) but generates a third stack that increases the cooldown to 8.5 seconds.

Why not "simplify it" to:
 * "Whenever Lustrum casts one of her basic abilities she empowers the next cast of that ability for 4 + (1.5 * current stacks) seconds. Each empowerment stack increases the duration of the ability and doubles the mana cost."

It means the cooldown of the ability always remains at 4 seconds, but the empowerment timer gets longer and longer. Given that it doubles the cost, you'll quickly run out of mana -> making the empowerment timer basically a second cooldown.