Events that use opt_in_setting: circ.default_overdue_notices_enabled
They use the following hooks:
Emailing checkout receipt uses opt_in_setting: circ.send_email_checkout_receipts
Events related to holds (including expiring holdshelf), booking reservation, checkin with missing pieces, recall do not use the opt_in_setting.
Depending on the trigger, the Processing Delay will be calculated differently. For example, triggers acting on an item due date count from 23:59 on the date something is due, while user account expiry counts from 00:00 on the date of account expiry.