After a new wife's opening nights, whose turn comes first?

After the seven nights (virgin) or three nights (previously married) for a new wife end, the ordinary rotation begins, and its order is decided by drawing lots or by mutual agreement.
The right to the opening nights is based on the hadith of Anas (Sahih al-Bukhari 5213; Sahih Muslim, Kitab ar-Radha'). After that, the husband may not keep extending his time with the new wife outside the rotation. In the Shafi'i school, to begin the cycle, the husband draws lots for who goes first so that no wife feels sidelined, following the spirit of the Prophet's ﷺ practice of drawing lots in Sahih al-Bukhari 2593. If all the wives agree on a particular order, that is also sufficient. See Fiqh of polygyny.