i haven't heard that they have a set time to release them on patch tuesdays......it seems they are released at all different times during the day from one month to the next. i would imagine they would definately be released by the end of the business day.....before 5pm.
edit: they're out now...1pm central time (u.s.)..i just got 6 of them(well, 6 high priority, and 1 software one).