Luanda to N'zeto can be made in just under 5 hours, the roads are good; either by public bus or by car which was my choice. It is advisable to make a break here and stay for the night, the best option is Perola do N'zeto, no reservation needed. Day 2 we did at an early departure N'zeto-Mbanza Kongo to visit the vestiges of the former Kongo kingdom (all walking distance including the very cute museum and the Royal cemetery)-and back to Luanda in the afternoon, covering about 700 kilometers.
The driver/guide was excellent, highly recommended; we hired him to the Calandula Falls (another highlight in Angola) as well. His contacts are What's up +244 925317932 Oscar.