What is the ruling on praying Maghrib with long surahs until the time for Isha enters, and is praying the post-Maghrib sunnah prayer after the time for Isha has entered considered a qada'?

The guidance of the Prophet, peace and blessings be upon him, concerning the Maghrib prayer was to make it light, and he would usually recite short surahs from Al-Mufassal. It has been reported that he also recited longer surahs in it, such as Al-A'raf, Al-Mursalat, At-Tur, Ad-Dukhan, and Al-Qital. Lengthening the prayer was a less frequent practice of his and did not cause the prayer to go beyond its prescribed time. Therefore, a Muslim should follow his Sunnah, peace and blessings be upon him, and always lengthening the prayer goes against his Sunnah. Indeed, the Prophet, peace and blessings be upon him, rebuked Mu'adh for lengthening it. If part of the prayer goes beyond its time, it can still be caught up with, based on his saying, peace and blessings be upon him: "Whoever catches one rak'ah of the prayer has caught the prayer." It is not permissible to intentionally delay part of the prayer beyond its time. If a Sunnah prayer is missed due to an excuse, it should be made up.