I am very new to this video editing, so sorry,...
I actually want a transition that takes longer to undip from black than to dip to black.
I wanted to add two transitions, one at the end of the first clip and have the transition stop at 50% and then another one at the beginning of the next and have it start at 50% and then adjust the time the transitions take.
It turns out one can only have one transition between clips. Which makes sense, but does not explain how I should proceed.