It depends , brother ..!! If you're going via Shimla route then 10 days are not enough to explore both the places and for spiti valley even 10 days are also less for explore. My suggestions is that you should drop the plan of Kasol and give your whole 10 days to Spiti Valley . You won't regret it.
More than sufficient. Take a day to acclimatise in Manali. The next day proceed to Spite by HRTC bus which should open anytime now. After 2-3 days return back to Kullu and make way to Kasol from Mandi. 10 days is generous for Spiti and Kasol. If possible take a drone.