Depending on the airport and the hour of your arrival, if you are arriving early in the morning or late at night, you can pick up your Pocket wifi at a different counter than the one during the day. The counter is determined by your time of arrival +2 hours.
Below is a list of reception counter for each airport:
Narita Terminal 1: 8:30 - 20:00 = The post office counter
Narita Terminal 1: 6:30 - 8:30 and 20:00 - Last flight = QL Counter
Narita Terminal 2: 8:30 - 20:00 = The post office counter
Narita Terminal 2: 6:30 - 8:30 and 20:00 - Last flight = QL Counter
Haneda Airport : 24/7 = JAL ABC Counter
Kansai Airport: 9:00 - 17:00 = The post office counter
Kansai Airport: 6:30 - 9:00 and 17:00 - 22:30 = JAL ABC counter
Chubu Centrair Airport: 6:30 - 21:30 = Yamato counter
New Chitose Airport: 9:00 - 17:00 = The post office counter
New Chitose Airport: 7:30 - 9:00 and 17:00 - 19:00 = New Chitose Temporary baggage storage
Fukuoka Airport: 8:00 - 21:00 = Yamato Counter
You will be contacted regarding the final information of the pickup counter 2 days before the start date of your rental, along with your tracking number.