I think Keegan Bradley's pre-shot routine is much longer than Na's. Na's problem is when he can't pull the trigger. But it seems like that's not happening very often right now. But like some others said, it's sometimes difficult to tell exactly how fast or slow someone is from watching on TV.
I'd like to see the PGA Tour release a list with everyone's times for their round. Pretty much everyone should be just about the same, but it would be interesting to see if there are any outliers.