SELECT "Date" FROM table_55414 WHERE "Edition" = '1991 world group i' AND "Opponent" = 'li fang'
When was the 1991 world group I with the opponent of Li Fang?
CREATE TABLE table_55414 (
    "Edition" text,
    "Round" text,
    "Date" text,
    "Surface" text,
    "Opponent" text,
    "Result" text
)