Smoga,
How long are you keeping the 1968 in primary and at what temp do you ferment? With a big starter (like in a commercial brewery) this yeast will go to FG in 4 days, but needs 6-7 days to clean up completely. That is what Wyeast is talking about. If you are fermenting at 66-68 for 7 days or longer, you don't have to worry about diacetyl.
Dave