Your plan's validity starts when the eSIM first connects to a local network at your destination.
- At purchase → the clock does not start
- At installation → the clock does not start (no data consumed either)
- First connection to a local network → your validity period begins here
So installing days or weeks in advance costs you nothing. Even with the eSIM line turned on at home, nothing starts until it connects to a network in your destination.
Related: How data allowance and validity work