Beyond "Time to Surgery": a structured evidence review and multi-clock framework for emergency cranial neurosurgery

Timing is often treated as a decisive variable in emergency cranial neurosurgery, but studies frequently use different temporal anchors, intervention endpoints, and outcomes under the same label of "early" intervention. This structured evidence review with narrative synthesis proposes a multi-clock framework for interpreting timing-to-intervention evidence across acute epidural hematoma, acute subdural hematoma, severe traumatic brain injury requiring decompressive surgery, and aneurysmal subarachnoid hemorrhage. We reviewed clinical guidelines, randomized trials, comparative-effectiveness studies, cohort studies, registry analyses, systematic reviews, meta-analyses, and methodological literature addressing timing and timing-related bias. Across the literature, timing was not a single exposure. Relevant clocks included injury or ictus onset, first medical contact, emergency department arrival, first neuroimaging, neurosurgical evaluation, treatment decision, procedural start, and effective intervention. These intervals captured different combinations of biological progression, recognition, transfer logistics, diagnostic access, clinical decision-making, system readiness, and procedural execution. Acute epidural hematoma showed the clearest biological urgency but limited contemporary comparative timing evidence. Acute subdural hematoma was most affected by confounding by indication and patient selection. In severe traumatic brain injury, decompressive surgery shifted the timing question from lesion evacuation to evolving intracranial physiology. In aneurysmal subarachnoid hemorrhage, the strongest ultra-early signal concerned rebleeding rather than consistent long-term functional benefit. Emergency cranial neurosurgery requires a shared temporal language rather than a single universal time-to-surgery metric.