When a single photon propagates through a cloud of two-level atoms, part of its energy is temporarily stored as a collective atomic excitation. This raises a fundamental question: is it possible to meaningfully quantify how long a photon ‘spends’ in this atomic state? If so, does this duration depend on whether the photon is ultimately transmitted through the cloud or scattered by the atoms? In our recent theoretical work (arXiv:2310.00432), we introduce an ‘atomic excitation time’ that can be measured by weakly probing the atoms and calculate this time for both cases. For transmitted photons, this time coincides with the photon’s group delay, which can be negative—a prediction we later confirmed experimentally (arXiv:2409.03680). For scattered photons, the excitation time equals the time delay of the scattered photon, varying from two atomic lifetimes to a negative value depending on where the photon scatters. In this talk, I will present these findings and discuss our plans to measure this excitation time as a function of scattering position.