Hi us4m4h
All of your questions are related to index in JA Megafilter.
When you update content, the new content is not automatically updated in mega filter pages, you have to re-save or index the mega filter from back-end.
The feature - Cron Job allows you to configure to auto index for specific mega filters (1 or more) in defined duration (the time is in miliseconds)
With the generated cron URL, you can setup a cron job in your server side, almost hostings have option to setup this.
Regards