Later in the same book, al-Quduri states that the legally qualifying time for the Arafat standing runs from zawal on 9 Dhu al-Hijjah until Fajr on 10 Dhu al-Hijjah. This defines the window for catching the essential standing.
The ordinary sequence described here for pilgrims present during the day is to remain until sunset and then depart for Muzdalifah. These are not identical propositions; a late-arriving pilgrim is a separate case.