While Christmas and New Year’s bookings are strong, periods before and after are weak, inspiring the 25-percent-off sale on Nov. 27 through Dec. 6, with rooms from $274, and 50 percent off spa services. Survival of the busiest is the invisible hand feeding Black Friday travel deals this year, which seem to be growing based on the number of first-time sales, deeper discounts and extra perks, all usually bundled with flexible cancellation policies. Notably this year, the Black Friday sale window has been expanded, not just to what is known as Cyber Week — the week following Thanksgiving — but to much of November. The online travel agency Expedia is lengthening its sale by five days this year, running through Dec. 1, often highlighting free cancellation policies.