Safety-Critical Delays in Vehicular Networks Toward 6G: A Novel Metric for Disconnection Time Assessment

5G and emerging 6G V2X systems aim to enhance road safety through reliable, low-delay sidelink communications based on Semi-Persistent Scheduling (SPS) and Dynamic Scheduling (DS). Conventional metrics focus on packet-level reliability and overlook the temporal structure of outage events. We introduce a novel timeliness metric, Disconnection Time (DT), which quantifies the duration of V2X communication interruptions caused by consecutive packet losses, particularly persistent collisions in SPS. DT reveals prolonged outages that may have a limited impact on average inter-reception statistics, but may significantly affect safety-critical control loops. Simulation results show that, seen through the lenses of the new proposed metric, DS can outperform SPS, even for periodic traffic, especially at short inter-vehicle distances. These results highlight the importance of temporally aware metrics for future goal-oriented V2X and 6G standardization.