What are the conditions for combining and shortening prayers (al-Jam' wal-Qasr) and what is the religiously permissible duration for doing so?

Shortening prayers (qasr) is specific to travel, whereby the four-rak'ah prayer is reduced to two rak'ahs, provided the traveler does not intend to stay during their journey or in the country they are traveling to for more than four days. There is no specific duration for combining or shortening prayers except for the period of the excuse that necessitates the dispensation.