Those patch notes are outdated. There was a thread discussing
Hydra, it's weaknesses, and how to improve it. The thread councluded that doubling the duration of Hydra only increased the number of counters and screen-clutter it caused, and still left the skill slow at building up its damage. The resolution was to give it a significant damage buff while reducing the duration to compensate. The end result is that the skill does more damage with 3 Hydras (the current max number at a time) then it used to do with 5 hydras. This means that you achieve maximum strength faster, and that strength is about 25% more than the original 12-second duration Hydra, while not incurring the penalties of the 24 second duration version. The duration will not be changed any time soon unless people find a problem where an increased duration would be a good solution while an increase in damage would not.