Regardless of the time of day you decide to fly, the ticket price will remain around the same. Book flights from San Francisco to Havana as you normally would.
SFO and HAV are unique codes to identify airports used in the aviation industry. They are defined by IATA (International Air Transport Association) and are commonly called IATA codes. SFO to HAV refers to a flight route from San Francisco Airport to Havana Jose Marti Intl Airport.