The optimal time to enter emerging industries is a key concern in strategy, yet scholars struggle to create a theoretical foundation that can integrate conflicting empirical findings. We incorporate categorical dynamics to industry life cycle theory to enhance existing entry timing theories. We introduce the concept of a dominant category—the conceptual schema that most stakeholders adhere to when referring to products that address similar needs and compete for the same market space—linking it to the dominant technological design and entry-timing advantages. In particular, we propose the existence of a window of opportunity for firm entry that starts with the emergence of the dominant category and ends with the emergence of the dominant design.