فَإِذَا أَرَادَ أَنْ يَتَعَجَّلَ النَّفْرَ نَفَرَ إِلَى مَكَّةَ
Translation: If he wishes to depart early, he departs for Makkah.
Yataʿajjala al-nafr means choosing the earlier permissible departure after the obligatory stoning on the 12th. A pilgrim who makes the legally valid departure does not perform the optional additional day's stoning on the 13th.
The phrase is not permission to skip the 12th's stoning and leave in the morning. The departure is understood in the sequence after that day's prescribed rite.