In the constitution, it says that: "The President shall have Power to fill up all Vacancies that may happen during the Recess of the Senate, by granting Commissions which shall expire at the End of their next Session."
If it is argued successfully, and it has been, that a recess of one day is enough to allow a recess appointment, it could be argued that one day of senate session is enough to be the next session, becuase the Senate could have confirmed a nominee during that time.
Thus recess appointments should only last until the beginning of the next senate recess. If at that time, a new appointment has not been confirmed, another one could be made. That would be politically awkard though. Can this argument be made, and who can make it?