Hi all!
Thanks to user reports, we have identified an issue in how we were recording playtime in our Nintendo Channel database (see here for more info). The summary is that we have had to delete all previous entries in our database to resolve this issue on our end. To get your correct playtime data to show up in Checkout, simply delete your existing Nintendo Channel save data, then open the channel, making sure to opt-in to data sharing.
Apologies for the inconvenience this causes.