User blog comment:Willbachbakal/(Champion Rework) Zilean, the Chronokeeper/@comment-3297251-20130806065336/@comment-1330314-20130806114356

I increased the mana cost on his E to 120 mana and decreased its damage so that it's equivalent to a grab at level 1. That way, it'll also deal the same damage as a level 1 Time Bomb, even though the scaling's higher and the ramp-up's faster (though the cooldown also stays much higher as well).

The 50% bonus CDR is there as a substitute for Rewind, which let you spam two Qs and two Es instantly. This one isn't quite as spammy, but is instead more consistent and higher-risk (you need to stay in a small area to benefit from the bonus). Since this is not factored into cooldown reduction, it lets other players cast spells a lot faster, even with full CDR, and lets Zilean benefit from cooldown reduction as well.