You are correct: this cannot be changed from the front end. It can only be changed on the backend.
The schedule is defined in the “hooks.py” file for Frappe Framework (link here)
- The function
'frappe.email.queue.flush'processes all the emails in theEmail Queue. - The “all” schedule is configured via a JSON file. But by default, it’s every 4-5 minutes. (very confusing name for a schedule)
So. Let’s say we want our emails processed every 2 minutes instead? You could delete that line from “hooks.py”, and add your own. See my example below, using cron syntax.

