There is no definite answer to this question as the Affordable Care Act (ACA) does not specifically require insurers to provide a certain number of days notice before cancelling or changing a policy. However, the ACA does require insurers to provide policyholders with a grace period of at least 10 days in which to make any past-due payments before their coverage is terminated. Additionally, insurers are required to give policyholders advance notice of any material changes to their coverage (such as an increase in premiums or a change in benefits), and they are generally not allowed to retroactively cancel coverage except in cases of fraud or non-payment.