Buy early, but check the start rule
You can prepare before travel, provided the selected plan’s activation rule and installation window fit your dates. Some plans start on installation, others on a supported network connection, and some products have purchase-based timing.
Read the rule shown for your selected plan before buying or installing. If it is unclear, ask support first rather than assuming that validity waits until you land.
After delivery, save access to your private eSIM page and installation email. Install using a reliable internet connection when the plan’s instructions allow it. Do not activate early if that would use your travel validity.
At your destination, turn on the travel eSIM, select it for mobile data and enable roaming for that line. Keep roaming off on your regular SIM if you want to avoid its roaming charges.