I looked up ‘crepuscular’ on WordNet (v.3.0). It says ‘crepuscular’ means ‘ช่วงโพล้เพล้’ (twilight; =time just after sunset or time just before sunrise). Crepuscular animals are those active at dusk or dawn. Crepuscular plants takes advantages of abundance of pollinators at dawn and dusk. Some plants (eg. dragon fruit; ดอกราตรี/night blooming jasmine/Cestrun nocturnum) rely on pollinators (like moths and bats) at night.

So nocturnal = night; diurnal = day; crepuscular = dawn or dusk (between day and night)