Responding to the question, Sheikh Ahmad Kutty, A Senior Lecturer and an Islamic Scholar at the Islamic Institute of Toronto, Ontario, Canada, states the following:
Muslims are allowed to make qasr if they are travelling more than 80 kilometers. Qasr is allowed while they are away, but doing jam’ (combination) cannot be justified unless they are actually travelling, or unless they have a pressing need to do so. In other words, if a Muslim nurse or doctor is busy making rounds to see patients, then he is allowed to make jam’. But he is definitely not allowed to do so if he is not busy with patients, and he can take time for each prayer in their appointed times.
Moreover, this jam’ is only allowed between dhuhr and asr by praying them either at the time of dhuhr or asr, and between maghrib and isha by praying them either at the time of maghrib or isha. You are not allowed to combine asr with maghrib or isha with fajr or fajr with dhuhr.