https://community.expensify.com/discussion/13860/888-829-1467-can-i...
Yes, as per the DOT guidelines, an airline operating in the United States has to offer a risk-free time period of 24 hours from the initial booking. A passenger can enjoy free United Airlines cancellation and full refunds on any trips cancelled during this time. However, a passenger has to ensure that a gap of seven or more days remains between their booking and scheduled flight departure.