We investigated emergence of marine benthic harpacticoid and cyclopoid copepods from subtidal sediment into the bottom water. Previous studies that used traps in the field found that copepods emerged from the sediment within 2 h of dusk. We examined emergence in 20-min sampling periods over 13 h from 1200 to 0100 h in a laboratory flume under conditions of constant flow speed. The light intensity was adjusted to field conditions every 20 min. We observed a peak in emergence during the 20-min sampling period after the onset of darkness, greatly increasing the accuracy with which the timing of emergence is known. This result will help to set the stage for studies of emergence cues.