30 seconds x 0.55 (45% CDR) = 16.5 seconds
16.5 seconds x 0.6 (Cloud Drake 40% Ulti CDR) = 9.9 seconds
9.9 seconds x 0.75 (Ultimate Hunter 25% Reduction) = 7.425 seconds
Or something like that.
HERE HAVE MORE MATH
Ult CDR (Cloud Drake, Hunter) sits in a different bucket than regular cdr. Ult and regular multiply with each other (rather than adding the numbers together) to get your final ult cdr. Here's the extreme case which requires:
- A fully stacked Ultimate Hunter from Domination
- Cosmic Insight from Inspiration
- 40% CDR
- The elemental rift being Cloud
- The enemy team getting drakes 1 and 2 (which can't be Cloud), and you getting 4 out of drakes 3-7 (which are all Cloud)
Regular CDR: 5% from Cosmic Insight + 40% from other sources = 45%
Ult CDR: 40% from Cloud Drake + 25% from Ultimate Hunter = 65%
So your ult cooldown = (100%-45%) * (100%-65%) = 55% * 35% = 19.25% of its original. For Gnar that's 5.775 seconds so OP was basically right.