Enchantment Lenghths

Lets say you have a weapon that increases enchantment lengths by 20%,
and a skill that increases enchantment lengths by 30%. I want to know
which scenario is correct on how the enchantment lengths are applied.
Assume the length of the enchantment we are using has a base of 20
seconds.

Scenario A - The 20% increase from the weapon is applied, making the
enchantment 24 seconds. Then the 30% increase from the skill is applied
to that 24 second enchantment making the enchantment last 31.2 seconds.

Scenario B - The 20% and 30% are added together to make the 20 second
enchantment last 50% longer, or 30 seconds.

Scenario C - Only the larger of the numbers is used, and the 20 second
enchantment goes up 30%, to 26 seconds.

That's what happens. Duration effects multiply. I'm not sure how the game handles fractions of a second on durations.

I'm pretty sure it rounds up to the nearest tenth of a second, except for a few skills (I think Patient spirit rounds up to 3 seconds with a +20% mod)

I thought it was B because on the wiki where it has all the caps of stats, Enchantment lengthening is capped at +50%. Thats why I always used to go for +30% on Blessed Aura and +20% weapon to reach max.

Percentile values stack multiplicatively. Sam6555, where did you find that information? I don't see it on the effect stacking wiki page.