In traditional East Asian timekeeping, a 24-hour day is divided into 12 two-hour blocks named after the 12 Earthly Branches: Ty (11pm–1am), Suu (1–3am), Dan (3–5am), Mao (5–7am), Thin (7–9am), Ty/Snake (9–11am), Ngo (11am–1pm), Mui (1–3pm), Than (3–5pm), Dau (5–7pm), Tuat (7–9pm), Hoi (9–11pm).
"Auspicious hours" (gio hoang dao) are blocks folk tradition considers favorable for starting something important, travel, opening a business, signing a contract, a wedding, as opposed to "inauspicious hours" requiring more caution. Of the 12 blocks in a day, typically 6 are classified auspicious and 6 inauspicious, depending on that day's Branch (different day-Branches produce different sets of auspicious hours).
Traditional lookup tables group the 12 day-Branches into 6 symmetric pairs (e.g., Ty-Ngo, Suu-Mui), each pair sharing a fixed set of 6 auspicious hours, a folk convention passed down through almanac books, not an astronomical calculation.
Because this table is a folk convention and can vary slightly between different almanac sources, it should be treated as one reference factor among several (also considering the individual's age/zodiac and the type of activity) rather than the sole deciding factor.
Like day selection, auspicious hours are a general guide for starting activities; for especially important moments (a formal ceremony's exact timing, groundbreaking, a bride's arrival time), careful practitioners cross-check further against the specific individuals' ages rather than relying on the general auspicious-hour table alone.
