You will need to prove coverage that covers the loan amount of the mortgage to close on the home. You simply need the coverage declaration page (the "dec page") to prove that you have bound coverage.
Your coverage will begin as soon as the closing is finished and you take ownership of the property.
Founder, City Building Owners Insurance, Somers, NY
The amount of insurance may be determined by the insurance company, computing the replacement cost of the property, or by the lender, if more, to insure their interest in the property. At a minimum, your policy will need to cover the mortgage to protect the lender's interest. Your insurance company will help you figure out the coverage amount needed to protect your interests in the event of a loss.
Your coverage will begin as soon as the closing is finished and you take ownership of the property.