Google shows 7 hours approx for plains type roads only, but due to road construction work going on can delay it. Other than this, hill drive is slower and if you start early, it will be easy to reach in daylight.
Take 10 hours + for a enjoying drive in natural environment.
Joshimath to Karanprayag is construction zone for Road widening. You can start early to avoid any jam or delay here.
From Karanprayag onwards road will be curvy and you will be slower.
If there is no rains in this period then you can go easily without any landslide etc.
Google Maps :
From Joshimath, Uttarakhand 246443 to Kausani, Uttarakhand 263639 via NH 7 and Karanprayag Gwaldam Bageshwar Almora Nainital Rd.