Amazon Will Cancel Your Delayed FBM Orders - September 09, 2020

Amazon automatically cancels orders if they have not been shipped and confirmed within 30 days of the estimated ship date (ESD).

To protect and improve the customer experience, starting September 30, 2020, Amazon will automatically cancel any order that is not shipped and confirmed within 7 business days after the “ship by” date detailed in the “Sold, ship now” notification email. You can set this date by modifying your Handle Time, but please be aware this date is part of the delivery time calculation displayed on the offer listing and checkout page.

Reference: Modify handling time (Login Required)