When does the validity period start — when I buy it, when I install it, or when I land in Peru?

Validity on the ETravelSim Peru eSIM starts the day you start using it in Peru, not the day you buy or install it. You can purchase weeks ahead, install the QR code at home before you fly, and the timer only begins once your phone connects to the Entel network on arrival. This is the safer option than installing on arrival — you'll know before you board the plane that the eSIM is set up correctly. Just don't delete the profile after installation; reinstallation may not be possible.