Many protocols rely on the assumptions on the physical properties of the environment in which its protocol sessions will be carried out. For instance, Distance Bounding Protocols take into account the round trip time of messages and the transmission velocity to infer an upper bound of the distance between two participants. We investigate the foundational differences and the impacts on the protocol analysis when using models with discrete time and models with dense time. This is joint work with Max Kanovich, Tajana Ban Kirigin, Vivek Nigam, and Carolyn Talcott.