He (meaning the Prophet ﷺ) remained standing until the sun set, the yellowness faded a little, and the disk disappeared. The hadith continues.
فلم يزل (يعني النبي ﷺ) واقفا حتى غربت الشمس، وذهبت الصفرة قليلا حتى غاب القرص… الحديث.
Muslim narrated it in the chapter on Hajj (1218) via Hatim bin Ismail Madani, from Jafar bin Muhammad, from his father, from Jabir, who related it at length concerning the Prophet's ﷺ Hajj. The valid standing is that which occurs after the sun passes its zenith until sunset, as established by the practice of the Prophet ﷺ.