How can one combine the Maghrib and Isha prayers due to the nature of military work that coincides with the entry times of both prayers?

It is obligatory to perform all prayers at their prescribed times, and it is not permissible to offer them earlier or delay them except for a valid excuse such as travel or illness. Therefore, pray Maghrib and Isha at their due times. Isha can be delayed until before midnight if it is difficult to perform it at the beginning of its time. If you are unable to perform the prayer at its time and are prevented from doing so, there is no sin in combining Maghrib and Isha with a delayed combination (jam' ta'khir), based on the hadith of Ibn Abbas in Sahih Muslim regarding the permissibility of combining prayers while resident due to need, provided that this is not taken as a regular habit.