Which time zone counts for this Amtrak cancellation deadline?

What time zone does the Amtrak cancellation policy adhere to? That’s what Sonia Thacher and her mom want to know. 

Sonia booked a trip to the Grand Canyon with Amtrak Vacations and wisely included trip insurance with her purchase. But when she fell ill and was hospitalized, her mom canceled the trip. She did so before noon on the day the policy required in order to qualify for a full refund. So why is she being told she missed the deadline?