The US Department of Transportation requires airlines to offer consumers either 24 hour holds or 24 hour refunds for tickets they sell which are purchased at least a week in advance of travel.
United and Delta have offered 24 hour refunds even day of travel, not limiting the “courtesy cancel” benefit to reservations that are at least 7 days prior to departure.
United e-ticket confirmations now include a 7 day requirement describing the benefit, while United’s website does not.