Point to point its probably about 20 minutes or so. If you are driving when you leave the airport you make a right. You will drive about 2-3 minutes, you will pass a Texaco Station on the right and a little while later Advantage and Payless rental car. You will come to a point where you can either stay to the left and go into the city of Santo Domingo or to the right to go to San Pedro and La Romana. Stay towards the right, that highway will take you staright to Juan Dolio, you cannot get lost.
If you get to a toll booth, you went the wrong way, make the U-Turn before the toll, it is allowed and follow the signs towards the aforementioned cities to the left.