does all of japan have the same time zone
Japan Standard Time or JST (日本標準時, Nihon Hyōjunji, or 中央標準時 Chūō Hyōjunji) is the standard timezone in Japan, 9 hours ahead of UTC (i.e. it is UTC+09:00). There is no daylight saving time, though its introduction has been debated several times. During World War II, it was often called Tokyo Standard Time.
Japan Standard Time