You can purchase and install the eSIM now, but it will only activate upon your arrival in Japan. The plan’s duration is based on Japanese Standard Time (JST). A “day” is defined as a calendar day from 00:00 to 23:59 JST. For example, if you activate the eSIM at 23:00 JST, the first day will end at 23:59 JST, regardless of the actual usage time. Please note that late activations will result in shorter usage time for the first day.