What are the conditions for permissibility when combining prayers during the time of the second prayer?

Primary text

If combining prayers is done during the time allotted for the second prayer, the excuse must be present until the entry of the second prayer's time. If the excuse ceases during the time of the first prayer—such as a sick person recovering, a traveler arriving, or rain stopping—the combination is not permissible because the cause has been removed. If the excuse persists until the entry of the second prayer's time, combination is permitted, even if the excuse ceases after that point, because both prayers have become mandatory obligations upon the person's responsibility, and both must be performed.