In which cases does the cache become invalid ? Is this e.g. scheduled and if so, with which setting can this be configured ?

There are different types of cache, each of them is invalidated using different triggers, usually caches are cleared at different times depending on the situation, like data update. However all caches (in caches folders and in user's browsers) by changing revision number in Studio > Developer > Settings

Is there a method to rebuild the cache ? Keyword : WarmUp.

Caches are building upon first access, for example pages - different pages have own caches, but generally if you browse several main pages it will rebuild caches for them, it will include caches for these individual pages and some common caches as well.