We say not. While you may have free travel insurance cover on your credit card, we still recommend taking a specific policy for your travel, especially if it is going to be longer than a few weeks.
Booking tickets and planning, sure up until you get on the plane, or boat, use the credit card coverage (Within the constraints of your cover, travel duration could be a trap if it's a long trip). Once you step on the plane have your real cover in place.