The number of days you need to travel to the Dominican Republic really depends on your travel style, budget, and the places you want to visit.
If you only have a short amount of time, you can still see some of the country’s highlights in as little as 5-7 days. For example, you could spend a couple of days exploring Santo Domingo’s historic Zona Colonial, then head to Punta Cana or La Romana for a few days of beach time, and end with a day trip to the Samaná Peninsula to see the El Limón waterfall and the humpback whales (during whale watching season).
If you have more time, say 10-14 days, you can explore more of the country’s diverse regions, including the mountainous interior and the northern coast. You could spend a few days hiking in the Cordillera Central, then head to the beaches of Las Terrenas or Cabarete for some water sports, and end with a visit to the colonial city of Puerto Plata.
Of course, if you have more time and want to see everything the Dominican Republic has to offer, you can easily spend several weeks or even months exploring the country. It really depends on your interests and how much time you have available.