Photoperiod is a fundamental environmental cue that sets circadian clocks, shapes development, behaviour, and metabolic regulation; however, its role during oviparous elasmobranch embryogenesis remains largely unexplored. The epaulette shark, Hemiscyllium ocellatum, is a small reef-associated, oviparous species known for its resilience to environmental stressors, making it a valuable model for examining early-life developmental plasticity. We compared embryos reared under baseline light-dark photocycle (12L:12D) with embryos reared in constant darkness (0L:24D), to test whether the absence of light cues alters the timing and coordination of key morphological, respiratory, and energetic milestones. Embryos in both photoperiod treatments progressed through seven distinct developmental stages, however, from stage 4 onwards the onset of each developmental stage was considerably accelerated in dark reared embryos, culminating in an overall reduction in total developmental time by approximately 21%. Towards the end of stage four, a major physiological transition occurred and embryos shifted from passive, tail-driven ventilation to active buccal pumping. Under constant darkness this transition occurred approximately 30 days earlier. Growth and yolk utilisation varied across developmental stages in both treatments. Although all embryos reached 50% of their final body length at comparable proportional developmental stages, dark reared embryos reached 50% yolk utilisation 44 percentile points earlier than embryos reared under baseline photoperiod. These findings demonstrate that the absence of photoperiod cues accelerates embryonic development and alters the timing of key physiological milestones, with potential consequences post-hatch. This indicates that disrupted light regimes may influence early-life development, and post-hatch outcomes in other oviparous marine species. As coastal habitats increasingly experience altered light conditions due to turbidity, artificial lighting, and habitat degradation, understanding how embryos respond to disrupted photoperiod cues is essential in assessing early-life vulnerability and resilience of reef-associated elasmobranch species.