Time-measurement systems such as a circadian clock and a timer exist in animals. In the cricket, Gryllus bimaculatus, the male has the time-fixed post-copulatory sexually refractory stage (RS2, about 1 h) which occurs between spermatophore preparation and the start of a calling song. RS2 is shortened at higher temperature and lengthened at lower temperature, but not influenced by females or sensory afference from the genitalia. Protein synthesis and hormonal substances are not involved in the timekeeping for RS2. The timer for RS2 is located in the terminal abdominal ganglion. The main function of the timer is to inhibit courtship while the new spermatophore is formed in the genitalia which lasts about 40 min. In addition, the timer may be involved in spermatophore formation itself via the control of genital motoneurons innervating the genital organs serving as a template for the spermatophore. The reasons why the timer instead of peripheral feedback is used for spermatophore formation, the manner of spike output in timer neurons and the biochemical mechanism of timekeeping are discussed.