Kai recommend five to ten seconds, and five seconds is short enough
that I get timeouts when testing that are hard to distinguish from
having screwed up my content security policy.
The Kai Store makes display of advertisements provided by the KaiAds API
mandatory. I don't want such adverts to be inconvenient for the users,
so I've just gone for adding a menu item that will display one. This is
probably a little too crude, but it's good for testing things.
The actual KaiAds API code is not free software, so it's not included
here. My intention is to add it by hand to the Zip files for Kai Store
uploads. Without it, the advertising code does nothing.