The durability and quality of software contributions are critical factors in the long-term maintainability of a codebase. This paper introduces the Time to Modification (TTM) Theory, a novel approach for quantifying code quality by measuring the time interval between a code segment's introduction and its first modification. TTM serves as a proxy for code durability, with longer intervals suggesting higher-quality, more stable contributions. This work builds on previous research, including the "Time-Delta Method for Measuring Software Development Contribution Rates" dissertation, from which it heavily borrows concepts and methodologies. By leveraging version control systems such as Git, TTM provides granular insights into the temporal stability of code at various levels ranging from individual lines to entire repositories. TTM Theory contributes to the software engineering field by offering a dynamic metric that captures the evolution of a codebase over time, complementing traditional metrics like code churn and cyclomatic complexity. This metric is particularly useful for predicting maintenance needs, optimizing developer performance assessments, and improving the sustainability of software systems. Integrating TTM into continuous integration pipelines enables real-time monitoring of code stability, helping teams identify areas of instability and reduce technical debt.