Is it permissible for me to shorten the Dhuhr prayer and combine it with the Asr prayer, a "gathering of advancement" (jam' taqdim), given that I am a teacher who travels 120 kilometers to return home, and I arrive before Asr with sufficient time? And is it a condition that the shortening or combining of prayers be outside the city limits?

What a traveler returns from on the same day is not considered travel, even if it takes ten hours. Therefore, the concessions of combining and shortening prayers are not applicable. The listener must respond to the adhan (call to prayer) unless there is an excuse. As a precaution, teachers who travel a distance of 150 km daily should neither shorten nor combine prayers, because this is not considered travel in the common understanding of people. Combining prayers is only permissible when there is hardship in performing each prayer at its designated time.