The mechanisms involved in triggering hatching behavior in the katydid Eobiana engelhardti subtropica (Orthoptera: Tettigoniidae) remain largely unknown. Therefore, in this study, I aimed to clarify the mechanism of hatching behavior triggered by a light-on (L-on) signal. Hatching under transition from continuous darkness to continuous light (i.e., L-on step, dark pulses, and photoperiods) was concentrated within 2 h after the L-on, indicating that it was triggered by the L-on signal. Furthermore, hatching was directly triggered by a single L-on signal. However, the time from L-on to hatching under dark pulses and photoperiods was affected by the duration of the dark period. This dependency on the dark period’s duration before L-on indicates that it differs from the hatching trigger under the L-on step. The time from L-on to the earliest hatching time and the mean hatching time were similar under dark pulses and photoperiods. Those times were also similar at 15 and 20°C. This suggests that the time from L-on to hatching under dark pulses and photoperiods exhibits temperature compensatory properties, a characteristic of biological clocks. The time ranges from a few minutes to several tens of minutes; however, it is suggested that it is controlled by a time-measuring mechanism involving dark periods. Although it is well known that the L-on signal is involved in the time-measuring mechanism, to the best of my knowledge, this is the first study to report that the time-measuring mechanism is involved in the triggering of hatching behavior based on the L-on signal.