You should install (not activate!) your eSIM as soon as possible after purchasing your plan. You can activate your plan when you are ready to use data either by clicking the "Activate Now" button on the website or iOS app or by turning on the line and start using data. The way to activate data depends on the specific plan and is detailed in your installation instruction.
If you need to access the Nomad website/app to activate data, you will need a stable connection, so please consider doing it before arriving at your destination.
Check out our website: getnomad.app