Another oft looked over featuer of the markets is price discovery. By compressing when all the participants participate, it allows all the buyers and sellers t

Another oft looked over featuer of the markets is price discovery. By compressing when all the participants participate, it allows all the buyers and sellers to come to an agreement on price with the most information participating. At least that's the theory. When looking at off-hours trading data, differences in opinion cause wild swings that then normalize during the 9:30-4 window. Technically, there's no reason that the markets can't participate 24/7, but the Nasdaq operates from 4a to 8p, and the crash that occurs at 9:30 still occurred despite markets being available for participation between 4a to 9:30a.