Miami and Havana are usually on the same time. Miami uses Eastern Time (EST/EDT, UTC-5/-4) and Havana uses Cuba Time (CST/CDT, UTC-5/-4). When it's 12:00 PM in Miami, it's typically also 12:00 PM in Havana.
Both cities observe daylight saving time, though Cuba's DST schedule may differ slightly from the US schedule, causing brief periods of 1-hour difference.
Any time generally works! Since both cities usually share the same time zone, you can call during normal business hours (9:00 AM - 6:00 PM) without conversion needed.
Miami and Havana are remarkably close - only about 230 miles (370 km) apart, making it one of the shortest distances between the US and Cuba. Miami has the largest Cuban-American community in the United States. Flight time is only about 1 hour.