The traveler may pray the travel (shortened) prayer once he has passed the city limits

The view of the majority of scholars is that the traveler
is allowed to pray the travel prayer (i.e., shortened) once he has passed
the city limits, because the Prophet

(peace and blessings of Allaah be upon him) used not to shorten his
prayers when traveling until he had left Madeenah. Then he would pray
two rak’ahs, because what matters is the time when the action is done.
If the muezzin gives the adhaan for Zuhr or ‘Asr, and the traveler sets
out and passes the city limits, then he is allowed to shorten the four-rak’ah
prayer. What counts is the time when the action is done, not the time
when he left the city, because at the time when he does the action he
is traveling.