I was told that it starts when the car was built and the built date is
considered to be January 1st of the year of the model, so that it
would be January 1st 2020 for a Camry 2020. Is this true?
When does the manufacturer warranty for a car start?
The term of a manufacturer's warranty on a new motor vehicle is defined in the written warranty contract that accompanies the sale, but the definitions used are fairly uniform as a matter of industry custom and practice (and influenced by various regulatory requirements). The language defining the warranty term from a warranty for a 2018 Acura (I picked it at random as an example) is pretty typical. It states in the pertinent part:
Time and Mileage Period
This warranty begins on the date the vehicle is put into use in one of
the following ways:
• The vehicle is delivered to the first purchaser by an Acura dealer.
• The vehicle is leased.
• The vehicle is used as a demonstrator or company vehicle.
Your vehicle is covered for 4 years or 50,000 miles, whichever comes
first. Some parts may have separate coverage under other warranties
described in this book.
So, suppose that you buy a car with a 4 year/50,000 mile warranty from a dealer on February 14, 2021 when it has 17 miles on the odometer. This warranty expires on February 14, 2025 or when it has 50,018 miles on the odometer, whichever comes first.