Is it permissible for a traveler to combine and shorten the Maghrib and Isha prayers when stopping at a station, if he will catch the Isha prayer in his hometown?

It is not a condition for Salat al-Jam al-Taqdim (combining prayers by performing the second prayer at the time of the first) that the excusing factor for it persists until the time of the second prayer begins. So, if the excuse ceases after performing both prayers at the time of the first, and before the time of the second prayer commences, then the prayer is valid and sufficient. It is permissible to combine Maghrib and Isha, even if one arrives in a country when the time for Isha has already begun.