There are often times when emitted methane is not blown toward any of the CMS sensors on a given site, which we will subsequently call "non-detect times." During these times, the sensors will not record enhanced methane concentrations, making it incorrectly appear as if no emissions were occurring. In a simulated one-source scenario, Chen et al. find that non-detect times make up 78% of total time when using one CMS sensor and 45% of total time when using four CMS sensors. Non-detect times can cause a delay between emission onset and detection, ranging from 12 hrs on average using one sensor to 4.3 hrs on average using four sensors on a typical tank battery. In this work, we propose the Probabilistic Duration Model (PDM), a method for directly estimating methane emission durations using CMS that accounts for non-detect times. We apply the PDM to CMS data collected during blinded controlled releases at the Methane Emissions Technology Evaluation Center (METEC) to demonstrate its practical feasibility.