Using your credit card coverage, usually begins immediately after you purchase the trip (e.g., flights, hotels, or vacation packages).
This applies to cancellations due to covered reasons occurring before your departure.
Other coverages (e.g., Baggage Delay, Travel Delay, Accident, or Medical Insurance) coverage generally starts when your trip begins, such as the moment you leave your home to travel to the airport or start your journey.
Unless someone can name a particularly policy they've used it seems a bit of minefield.