GG trains served the World's Fair spur daytimes and evenings, extended from the normal terminal at 71st-Continental Ave. E trains also served the spur from 8:24 PM until 1:00 AM to carry homeward bound crowds, alternating with the GG. After leaving the Fair E trains stopped at normal express stops (Continental, Roosevelt, Queens Plaza) and terminated at Hudson Terminal (today's WTC).
Above information is from Frederick A. Kramer's book, Subway to the World's Fair.
Also note that the IND charged 10 cents for its World's Fair service. Exiting passengers had to pass through another 5 cent turnstile; boarding passengers paid 10 cents at the same turnstiles.