Should I activate the eSIM before international travel?

Install before you travel — yes. You can install the eSIM profile at home using a stable Wi-Fi connection (no need to wait until you arrive). Just make sure the download completes and you can see the ICCID under Settings → General → About.

Activate at your destination — recommended. Your plan's validity starts from the moment the eSIM first connects to a supported network at your destination. Installing it early doesn't start your plan, and it won't count down while you're still at home. So for the full validity period, wait until you arrive to switch over and turn on Data Roaming.

Important note: If your device is a China mainland version, it cannot be installed before you arrive — installation must be done at your destination while connected to local Wi-Fi.