Zero Discussion

Attacking should reduce the cooldown of all skills - Time Distortion, Time Holding and Time Rewind being the more critical skills to be affected by this.

Similarly, attacking should reduce the cooldown of all of the skills in the rest of the Combinations i.e. anything with a cooldown of 5 seconds, 10 seconds, 15 seconds etc.. So if you used Combination 4 -- Wind Cutter > Wind Striker > Storm Break, then used one full Combination 1 sequence, your cooldown should have decreased by an additional 3 * 3 = 9 seconds (I think?).

Hadriel

Referring to skills as A (Alpha) / B (Beta) 1,2,3,4 a/b/c, one combination you can actually do with not much cooldown is
A4a A4b A4c A1a B4a B4b B4c B3a
As long as you hit mobs on all 6 of Combination 4, you're only using A1a and B3a to fill in the gaps until you can tag again (which seems to be 3 seconds firm, no cooldown reduction allowed)
When I'm lazy, I just use the 2 keys (A4 and B4) and deal with "You may not use the skill yet" spam. Or I pause for a bit after A4a/B4a to let the tornadoes stack more damage on (in Dimension invasion they last long enough to take out an entire spawn of mobs, it's insane)

I guess 15 seconds is starting from A4a, and by the time you've done 5 other attacks it's reduced to 0 anyway.

A4 and B4 are both massive damage attacks that don't move the character so this is what I use on bosses. They also combo with each other so this way you're getting twice as many attacks of both.