eSIMs can be installed before or after arriving in Japan. Data will only start to be consumed from your bundle once data roaming is enabled and you are in Japan.

The validity period of a eSIM should be considered when travelling. eSIM and data bundles have different validity and expiry periods.

In short the information for validity and expiry is as follows.

The data bundle will expire once data consumption has been first started and at the end of your validity of the package purchased.

You can check on the status of your current eSIMs and data bundles by logging into your account and going to "My Orders" this will show you your expiry date and data balance.