For how long is the concession (qasr) in prayer permissible when there is hardship in performing prayers at their appointed times due to the distance of mosques?

Performing the prayer on time is obligatory. A traveler is permitted to combine prayers, and it is best for him to do what is easier for him. As for the resident, he must perform the prayer on time, and it is not permissible to delay it except for a legitimate excuse. The absence of nearby mosques does not permit delaying the prayer beyond its time, for the entire earth is a mosque. And whoever is far from the mosque such that he does not hear the call to prayer, is not obligated to pray in the mosque. He should pray in congregation, even if not in a mosque.