Is there a minimum amount of time needed in country c?

I am flying from Seoul, South Korea to Beijing for the 72 hour visa. I then plan to fly to Macau before going back to Seoul, in order to qualify for the visa. As long as the flight from Beijing to Macau is direct and non stop, it does not matter how long I stay in Macau, correct? Could I fly back to Seoul from Macau that same day?