I want to keep backups in such a scheme:
hourly backups - 2
daily - 2
weekly - 1
monthly - 1

As I investigated the config file, I found that tiered mode is what I'm looking for, but I don't understand what frequency (cron) I should set. Is this every hour, and it'll just calculate everything for me and save as I want?

Correct, the cron controls when backups are created. And the retention scheme controls which backups are kept.
So if you want to keep 2 hourly backups, you need to be creating a backup every hour.