<p>Zero-day vulnerabilities remain among the most impactful cyber threats because they involve undisclosed and unpatched software weaknesses. The longer these vulnerabilities remain undisclosed, the greater the risk and potential damage to businesses and individuals. While existing studies have enhanced our understanding of the discovery and disclosure of zero-day vulnerabilities, we still lack information on the factors that impact the duration of these vulnerabilities. The main objective of this study is to examine which factors impact the duration of zero-day vulnerabilities and to what extent. Using a dataset captured between 2018 and 2022, we fit a negative binomial regression model to explore the impact of exploit price, vulnerability class, attack vector, attack complexity, privileges required, and user interaction on the duration of zero-day vulnerabilities. Findings indicate that vulnerabilities involving improper input validation, affecting office productivity and security software, and with higher severity levels, decrease the duration of zero-day vulnerabilities. On the contrary, vulnerabilities that require no privileges or user interactions, affect development tools and operating systems, and involve more vendors increase the duration of zero-day vulnerabilities.</p>