As it turns out… it depends on the airline!
The Best Airlines To Buy a Last-Minute Ticket [Upgraded Points] – “Conventional wisdom says booking early is the best way to save on airfare, but last-minute fares don’t always follow the rules. When booking with some airlines, delaying your purchase might actually land you a cheaper ticket, while on others, prices climb the closer you get to departure. So, how much does timing really matter when booking a flight?”