Is it the case that the shortening of prayers (qasr) begins upon leaving one's homeland until returning, without a specified duration, as stated by the scholars of the Ibadi school of thought?

The preponderant opinion among scholars is that if a traveler intends to stay in a town for more than four days, he must complete his prayers, because by doing so, he is considered a resident. They based this on the Prophet's (peace be upon him) hadith, in which he did not permit the Muhajir (emigrant) to stay in the town from which he emigrated for more than three days, which indicates that anything exceeding that makes the person a resident. What confirms this is the hadith narrated by Al-Alaa bin Al-Hadrami from the Prophet (peace be upon him): "Three [days] for the Muhajir after the return."