Hazrat Muhammad bin Munkadir says that once the Noble Prophet (peace and blessings be upon him) was asked whether it is permissible to split and separate the missed fasts of Ramadan when making them up. He replied that yes, you can do so. Look, if any of you has a debt and pays it off in one or two dirhams at a time, will the debt not be considered paid? Allah Almighty is even more forgiving and merciful.