ACCORDING YOUR NICE EXPLENATION ABOUT THE DIN OF HALF SLAVE (MISHNA RISHONA, MISHNA HARONA) I CAN'T SEE A WAY THAT HALF SLAVE HAS TO DO "REHIYA". THAT BECAUSE IF HE IS OBLIGATE TO COME (WHILE HE FREE) AT MIDNIGHT (CHATZOT) HE RETURN TO BE SLAVE (ITS FIT THE rambam IN perush hamishnayot)
rafim, givatsmuel,israel
According to the Kesef Mishnah's explanation of the Rambam, as long as he has his freedom for any given amount of time, during that time he is obligated to bring the Korban. It does not matter that later he will revert back to being an Eved.
According to the third explanation of the Rambam (the Lechem Mishnah's understanding of Rav Avraham ben ha'Rambam), it does not matter that the Eved reverts back to the master's possession at a given point (such as midnight); the Rabanan were Mafkir that ownership with regard to the Eved's obligation to bring the Korban.
Kol tuv,
Y. Shaw