What is the cheapest day to buy Amtrak tickets?

https://discussions.trendmicro.com/en-us/forums/cleaner-one-pro/81aec38d-c38f-ef11-95f5-000d3a40ff72https://discussions.trendmicro.com/en-us/forums/cleaner-one-pro/81aec38d-c38f-ef11-95f5-000d3a40ff72 What is the cheapest day to buy Amtrak tickets?