In the past, most cards were for a period of 30 days from what I recall. I just checked since you made the point and my VISA is 15 consecutive days coverage in the US and 31 consecutives days coverage outside the US.
My Discover Card provides coverage for 31 consecutive says anywhere in the world and up to 45 days IF it is a card issued by a business for business use.
Always good to read the fine print.
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