"Snapshot" intervals and destination explained

Hi,

1 - backup interval set to 5 minutes has not backed up for over an hour now. i read through, "The Snapshot scheduling process uses the WordPress Cron (WPCron) system" etc.. But what exactly does this mean ? What in the world is WPCron and why does it not allow me to get he precise time intervals ? There must be changes, interaction or updates on the front end of the site ? changes like what exactly/specifically ?

2 - Backup runs only when I choose "run immediately" and hit "save snapshot". Nothing happens if i select "manual" and hit "save snapshot". Whats the difference between "run immediately" and "manual" ?

3 - After choosing and running a backup with "run immediately" and i go back into the snapshot see a "save only" option in the interval. What is this about ?

4 - I created and selected a dropbox destination but still see files in the default local "/wp-content/uploads/snapshots/" with my FTP program. I believe i read that once a dropbox etc. destination is selected, then automatically the local is NOT used. correct ? Then my screenshot has me a bit confused because it only refers to "local". Is the "max" amount of backups only for local or will this apply to the selected destinations as well ?

Any kind assistance in this would be greatly appreciated.

kind regards,

RC.