Well if you instantly know that you are dreaming when you fall asleep in REM, then it's a WILD.
But if I DILD on a WBTB I usually dream that I am in a different place and then suddenly realise that I am dreaming, so that's pretty "quick" I guess.
But it's really hard to say because it's hard to differ a normal thought in REM, from a dream if it's vivid.. oh wait it's the same thing Well almost anyway.