There will certainly be more educated replies, but I'll throw in my two cents.
As I've come to understand it, the length of time spent on the actual movement of the lift is something more related to a bodybuilding concern right along with things like "peak contraction" and whatnot.
I'd venture to say if you're lifting heavy and not cheating on your movements then "counting to four on your way down and two on your way up" or whatever shouldn't matter as much. Remember, mass gain and bodybuilding aren't one in the same.
Squat, Press, Pull, eat - as I'm sure you already know.