Upon entering Cuba, a visitor's Visa is only good for 30 days. This is the only time you're allowed to enter the country.
The hotel where you are staying, or the Cuban immigration office will be able to help you apply for a Tourist Card extension after your initial 30 days in the country have expired.
If approved, the extension would add 30 days to your existing Visa, bringing the total number of days you can spend in Cuba to 60.
All foreign nationals who need a visa to enter the country for tourism purposes are issued a Cuba Tourist Card (Tarjeta Turista), also known as a Cuba Tourist Visa.
Almost all visitors to Cuba must have a Cuba visa (tourist card) before arrival. However, with the right paperwork and an understanding of Cuba, citizens of certain nations can visit the island without a visa.