Acute stress reaction (ASR) is a trauma-sensitive, time-dependent response that should be distinguished from acute stress disorder (ASD), post-traumatic stress disorder (PTSD), and PTSD-risk constructs. Given the narrow window for early psychological care, this narrative review summarizes evidence on time-sensitive assessment and intervention across three post-trauma periods: the immediate aftermath, the acute phase (24–72 h), and the subacute phase (3 days to 1 month). Because instruments specifically validated for ASR are limited, the review also draws on evidence from acute traumatic stress symptoms, ASD screening, and PTSD-risk monitoring while interpreting these constructs separately. Based on available evidence and expert synthesis, we propose a preliminary staged framework. In the immediate period, identification should prioritize safety, orientation, communication capacity, and basic functioning. During the acute phase, symptom screening should combine quantitative tools with risk stratification. During the subacute phase, re-evaluation should focus on symptom trajectories, functional recovery, and referral decisions. Immediate-response approaches, including Psychological First Aid, PIE-based strategies, the 6C model, YaHaLOM, and iCOVER, may provide practice-informed strategies for stabilization, orientation, and restoration of perceived control; however, their evidence base derives mainly from guidelines, field experience, training evaluation, and implementation studies rather than clinical outcome trials. For selected high-risk individuals with persistent symptoms or marked functional impairment, trauma-focused cognitive behavioral therapy may offer clinical benefit, with selective use of eye movement desensitization and reprocessing, medication, mindfulness-based approaches, or social support as appropriate adjuncts. Wearable monitoring, ecological momentary assessment, and digital phenotyping may support dynamic monitoring but should remain adjuncts to clinical judgment. Current evidence is limited by military-derived models, methodological heterogeneity, scarce long-term functional outcomes, and insufficient validation in civilian healthcare settings. Future research should test and refine integrated pathways aligning assessment, stratified intervention, and longitudinal monitoring with critical post-trauma windows.