While there is a limited 4-day period during which all purchases can be rescinded in the state of Texas, such a grace period does not exist when it concerns the purchase of an automobile. It is a common fallacy in the state to believe that all purchases may be rescinded within a 3-day period.
In fact, the so-called Texas Cooling Off Statute, which falls under the Business and Commerce Code, Chapter 601, only applies under very specific conditions. Namely, the sale has to occur at a place other than the vendor's place of business. It was designed primarily to cover door-to-door sales.
The statute actually makes an exception for automobile sales in which the vendor has set up a temporary place of business, provided that the vendor does have a permanent business address.