The twelve shíchen (时辰) are named after the twelve earthly branches (地支): 子时 (11pm–1am), 丑时 (1–3am), 寅时 (3–5am), etc. They are still referenced in Chinese medicine, fortune telling, and historical dramas.
usage
In modern colloquial usage, 时辰 can mean 'the right moment' or 'one's appointed time,' as in the idiom 时辰未到 (the time has not yet come). It carries a slightly fatalistic or dramatic tone.