8 hours with three stops seems right. We did it with two stops before in that time.

If you're taking a van, plan on an 8-10 hour trip.

If you're taking a car, maybe 7-8 hours.

Once you know the route through the mountains, and are at least familiar with where those (*$&#^^* potholes are, 6 hours is possible... be careful in the mountains in Nueva... there are sections of road that are kind of rough, and we cut a tire on a sharp pothole there before. Still, it's a beautiful place to drive. If you're the type who likes greenery, plan your trip so that you pass through the area at around 7 am, so you can see the sights.

BTW, Manila to Tugegarao is around 500km. Buy a full tank before going because gas costs over a peso more once you get to Tugegarao.