logs/worker.error.log records when your scheduled jobs run.
Probably these run at some default time, here are notes and clues
Schedule jobs at particular date and/or time - #2 by JoEz
Scheduler Job Manager, a simple app to schedule jobs at a date/time - #3 by JoEz
(env) frappe@erpnext:~/frappe-bench$ find . -name ‘*.py’ | xargs grep send_daily
./apps/frappe/frappe/hooks.py: “frappe.email.doctype.auto_email_report.auto_email_report.send_daily”,
./apps/frappe/frappe/email/doctype/auto_email_report/auto_email_report.py:def send_daily():