Final answer:
A breach must be reported to the US-CERT within 1 hour of discovery to ensure rapid mitigation and assistance.
Step-by-step explanation:
According to the United States Computer Emergency Readiness Team (US-CERT) breach reporting guidelines, a breach must be reported within 1 hour of discovery. This ensures that the US-CERT can provide any necessary assistance to address the breach and mitigate the damages as quickly as possible. Organizations should have procedures in place to detect and report breaches in a timely manner, as adherence to this reporting timeframe is critical for national cybersecurity efforts.