وَإِنْ أَرَادَ أَنْ يُقِيمَ رَمَى الْجِمَارَ الثَّلَاثَ فِي يَوْمِ الرَّابِعِ بَعْدَ زَوَالِ الشَّمْسِ
Translation: And if he wishes to stay, he stones all three Jamarahs on the fourth day, after the sun has passed the meridian.
Al-yawm al-rābiʿ counts from 10 Dhu al-Hijjah as day one: 11 is second, 12 third and 13 Dhu al-Hijjah fourth.
The original time stated for this additional day is also after zawāl. A pilgrim remaining through the 13th stones all three Jamarahs again—21 further individual pebble throws.