As far as I am aware, you must make sure that your health insurance will cover you from the start until the expiry date of your visa, and that will be examined when it is being issued. But different embassies are VERY likely to have different views on the application of regulations. Better to get expert advice from visa specialists (they have websites for contact details). As someone else has said, you will need to show them your cover certificate before they will issue your visa. Good luck.