"There isn't a golden rule anymore," says Patrick Scurry, chief data scientist for Hopper, a travel-information firm that archives ticket prices. Airlines Reporting Corp., which handles tickets sold through travel agents, pinpointed Day 57 as when you'll find the cheapest average domestic fares. Expedia Inc. says for tickets bought at least 21 days in advance, Tuesday is still cheapest by a thin margin over Wednesday, but Sunday is better for tickets bought within 21 days of travel — an average savings of $12, or 2.2 percent, over buying on Saturday or Tuesday, according to Expedia. Virgin's flash sales are generally advance purchase for travel in a few weeks, so they are not practical for last-minute business trips. The experts say airlines know flights will be full, they know which days people want to travel — the Sunday after Thanksgiving, for example — so prices start high and stay there. — There are plenty of websites, apps and Twitter accounts that tell consumers about bargains on specific routes or sales.