This depends on the plugin or cache system being used, but it can be done ahead of time, yes. Generally, the cache is created on the first visit and purged when

This depends on the plugin or cache system being used, but it can be done ahead of time, yes. Generally, the cache is created on the first visit and purged when a change occurs. Highly dynamic pages can be excluded from the cache by default, like the login or the cart page on an E-commerce website. Some solutions even allow to change the caching period for specific parts of the code, on the fly (fragment caching).