Consumer protection regulations require that applicants be given three business days to cancel the account because of the security interest in the home. You cannot use the card until the cancellation period (also known as a rescission period) has expired.
This regulation was established by the Truth in Lending Act (TILA) under U.S. federal law, and allows a borrower to cancel a home equity loan, line of credit, or refinance with a new lender, within three days of closing.