About an hour and a half. No gas stop needed. But the roads are tricking. You can happily end up going to Santiago, as I did once, or to Pedernales, ditto, or to San Jose to Ocoa .. did not but coulda
So yeah, stop and ask for directions.. And BRING a MAP.. Do not depend on the Google on your smart phone.
Getting out of the city on the right road is one of the tricky parts.
Sweet town. Great hotel Called EL Libano