The increased complexity of programs and pro-cessors is an important challenge that the embedded real-time systems community faces today, as it implies substancial timing variability. Processor features like pipelines or communication buses are not always completely described, while black-box programs integrated by third parties are hidden for IP reasons. This situation explains the use of statistical approaches to study the timing variability of programs. Most existing work is concentrated on the guarantees provided by positive answers to statistical tests, while our current work concerns potential algorithms based on the negative answers to these tests and their impact on the timing analysis. We introduce here one such algorithm, the Walking Kolmogorov-Smirnov test (WKS).