You must check your eSIM’s activation policy.
Before purchase:
Search for the country you wish to buy an eSIM for
Select the eSIM that you like
Check the Additional Information
Tap “Show more” to find the Activation Policy
After purchase:
Go to My eSIMs> Details> Show more> Activation Policy
The activation policy will be either as follows
“The validity period starts when the eSIM connects to any supported network(s)”: This means that you can install the eSIM before traveling without activating it. Once you arrive at the destination you can connect by turning on your eSIM line as long as the setup has been completed as advised on your eSIM installation page.
“The validity period starts at the installation”: This means that your eSIM will activate instantly once installed, and hence, the validity period will start to run although you are not yet at the destination.