Preloading

If wp-cron works properly, the preload works properly as well.

So if you have 10 visitors per day, the preload can’t work as expected (6 per minute for me).

Right ?

Exactly.

https://codex.www.ads-software.com/Function_Reference/wp_schedule_event

…The action will trigger when someone visits your WordPress site, if the scheduled time has passed…