Chinese auspicious hour selection, 择时, 时辰吉凶, 黄道吉时, lucky hours, best time of day, 嫁娶吉时. Returns all 12 shichen (two-hour periods) of a date, each with its 宜 (favorable), 忌 (taboo) activities and 黄道/黑道 quality. Optional activity param returns the best hours for that activity. Pairs with /almanac/select: which day, then which hour. For AI agents handling event timing, wedding/ceremony hour selection.