Is persistence and regularity in performing supererogatory prayers sometimes between Dhuhr prayers and sometimes after Duha prayer, without adhering to a specific time, considered an innovation?

We have previously issued a fatwa regarding the persistence of observing vigils between Dhuhr and Asr. We did not definitively state that persistence is an innovation (bid'ah), but it may be an innovation or lead to one. There is no harm in performing voluntary prayers (nafl) occasionally between Dhuhr and Asr or during the forenoon (Duha), to avoid persisting in performing voluntary prayers at a specific time for which there is no Sunnah.