Fun fact: The default Start Menu pop-up delay in Windows XP was 400ms. Once of the first things I always did was reduce it to <100ms on every new machine I used.
While for you (and most of us here) that delay was too slow, it also served a purpose -- users who can barely hold the mouse would diagonally go from parent to e.g. 4th child element too slowly and lose the submenu on the way, because it would disappear after the same delay if cursor was not on parent-or-child. Otoh, windows devs could arguably make it independent and the problem could disappear.
In short, with 100ms you have to go ¬-shaped and with 400ms you can go \-shaped.
