SELECT "Time" FROM table_79599 WHERE "Heat" < '5' AND "Lane" = '5' AND "Nationality" = 'vietnam'
What is the time in a heat smaller than 5, in Lane 5, for Vietnam?
CREATE TABLE table_79599 (
    "Heat" real,
    "Lane" real,
    "Name" text,
    "Nationality" text,
    "Time" text
)