Is completing the recitation of the Quran over eight months at a rate of a quarter of a hizb daily, after the dawn prayer in congregation by the imam, considered an innovation (bid'ah)?

There is no impediment to completing the recitation of the Qur’an in this manner, provided that it is not accompanied by the belief that this specific manner is a Sunnah. This is because a Muslim may read and complete the Qur’an as it is made easy for him, whether in prayer or outside of it, even though completing it in this specific manner is not required. It is disliked for a carrier of the Qur’an (someone who has memorized it) to let forty days pass without completing its recitation.