Not sure how it is in pve, but I know it doesn't work in wvw ^^ I was testing and coming up with some builds for the new patch and realized the trait didn't change the duration like it says it does, same for the potency of alacrity.
I did a two simple tests to confirm this! By using well of calamity with the new trait stretched time + my gear I would get about 6 1/2 seconds of alacrity from the well, one with improved alacrity and with out, Well of calamity cool down would land my well cd the same with or without the trait change being 13 seconds when alacrity ended! Same for the duration of alacrity it stayed the same even though when you take it, it says +50% skill recharge rate. ;O
thankyou for reading :)