Debuff Expiration question

i have a quick question about the stat "Debuffs on you expire #% faster"
if a debuff lasts for 4 seconds, and you get 50% faster, does that mean it will still last 2 seconds, or 3 seconds?

if you can get debuffs on you expire 100% faster, would a 4 second debuff still last 2 seconds, or instantly expire/not be applied at all?

b

nobody knows the answer to this question?