This post is education only. We are not recommending any plan or provider and do not link to any.
Some trip protection benefits are only available if you buy within a set window after your first payment toward the trip. Squaremouth, a travel insurance comparison site, says these time-sensitive benefits are usually available within 10 to 21 days of the first trip deposit, depending on the policy. Examples it names include cancel for any reason coverage, pre-existing medical condition waivers and financial default protection. Once the window closes, you no longer qualify for those benefits.
Usually the first money you spend on the trip, often the airfare or a hotel deposit. That date is the start of the clock, not the day you started planning.
If you decide you do not want trip protection, nothing here changes that. The point is to make it a decision, not something that lapsed.