JMT NOBO from Red Cones to Happy isles – how many days?

Hello all I'm planning to do JMT section hike this september, and wondering how many days I should plan for the Red Cones - Happy Isles hike. We're average couple in mid-30's in average shape, don't regularly hike. From my research, it seems it takes normally 4 days without zero day (stay without walk), so I'm thinking maybe planning for 6 days would be safe bet plus some scenery enjoying. Any ideas? thanks in advance!