Learned timing looks at the customer’s own orders of a product over the last two years. With enough orders, 3 by default, it takes the middle value of their gaps per unit and uses it in place of the product period. The result stays between a quarter and four times the product period, so one odd purchase cannot move a reminder far. With thin history the product period is used.
Customer chosen interval adds a Remind me to reorder choice to the product page and the Reminders tab in My Account, such as every 3, 4 or 6 weeks. The choice beats everything else, does not multiply by quantity, and is remembered for that customer and product.
