Quote: A typical skyjacking of the day was the incident involving National Airlines Flight 1064 from Los Angeles to Miami. After a stopover in Houston, a Cuban identifying himself as R. Hernandez seized a stewardess, using a gun and an object wrapped in a handkerchief which was believed to be a grenade. "Fidel ordered me back to Havana, dead or alive" Hernandez reportedly said in Spanish. The pilot convinced the hijacker that the aircraft required a fuel stop in New Orleans before attempting the flight to Cuba. The New Orleans Police believed that they could not attempt recovery of the aircraft without risking the lives of the crew and passengers. The flight continued to Havana, where Hernandez revealed that his hand grenade was in reality a bottle of Old Spice aftershave lotion. Cuban authorities apprehended Hernandez, and released the crew to return the aircraft to Miami. A DC-6 chartered by the U.S. government returned the passengers to the U.S.
The second link on that results page gives the date of the hijacking as July 17, 1968. I'm not sure how long the passengers were in Cuba before returning to the U.S. but it probably wasn't very long.