I think your are correct, SB.
Let's assume a rule says: A person must not do X, if Y.
It follows that if Y does not exist, the rule does not prohibit the person from doing X.
Now:
- substitute for X: "act as, or perform any duties or functions preparatory to acting as, a member of the operating crew of an aircraft", and
- substitute for Y: "if the person has, during the period of 8 hours immediately preceding the departure of the aircraft consumed any alcoholic liquor".
It follows that if a person has not, during the period of 8 hours immediately preceding the departure of the aircraft consumed any alcoholic liquor, the person is not prohibited by (3) from acting as, or performing any duties or functions preparatory to acting as, a member of the operating crew of that aircraft, even if, for example, the preparatory act is 1 hour before departure and only 7 hours and 1 minute after the bottle.
Examples:
Bob consumes 1 beer at 2200 local. Bob departs in his aircraft at 0601 local the next day. (3) did not prohibit Bob from doing anything preparatory to the flight or otherwise at any time.
Bob consumes 1 beer at 2200 local. Bob depart in his aircraft at 0559 local the next day. (3) prohibited him from performing all duties and functions preparatory to and and departing on that flight.
Bob consumes 27 beers, the last of which was downed at 2200 local. Bob departs in his aircraft at 0601 local the next day. (3) did not prohibit Bob from doing anything preparatory to the flight or otherwise at any time. (However, Bob would be in breach of the general impairment rule.)