Sam2:- Possibly if the Matzo Mitzwoh is not all the way until Tzofun, but more probable that the Matzo Mitzwoh is the very 1st keZayis, in light of the fact that the Benediction “Al Achilas Matzo” is recited in conjunction with the very 1st keZayis.
If Tzofun would be the prime Mitzwah of Achilas Matzo, it wouldn’t only be very preferable to consume the Afikomon prior to Chatzos, but absolutely mandatory, in light of the fact that the Toroh precribes {in Parchas haChodesh} to meat Matzo “Bo’Orev” [conotation of evening and not the entire nite] unlike Korban Pesach whose time frame is “baLailo HaHu” [Keri’as haToroh of Shishi Shel Pesach].