That is a beautiful trip
I do hope you get in early enough to make the entire trip in the daylight.
there are a couple of tricky turns. One in Nagua and one in S?nchez. But it is hard to get lost.
The trip, done at a moderate pace should take you about three hours +/- 30 minutes.
Are you going to Saman? proper or Las Terrenas or Las Galeras.
If either of those is your destination, add another :45 to the trip.
HB