Every travel insurance company has different requirements as to when you must purchase the policies and what they will cover, which is why it's important to work with a reputable agent.
A Cancel For Any Reason policy is the most expensive one you can buy. Most of the time you really do not need this type of coverage, especially since it will not reimburse you for 100% of your trip costs.
Also, keep in mind that there is a HUGE difference between travel insurance and travel protection, so it's extremely important to make sure you are purchasing the insurance.
Make sure you get a copy of the policy before you buy it, read it carefully, and double check to insure it covers the specific items you are most concerned about.
And lastly, don't assume a big name insurance company offers the best policy. Cruise Planners use to sell policies from 5 companies, but they fired 3 of them because they did not offer good customer service to our clients. And two of those were the biggest names in the business! Selling a policy is one thing, but the type of customer service provided when you need to file a claim is what sets the companies apart.