You can do Kapuche glacier lake trek within 4 days from Pokhara. But you can complete it in 3 days as well if you are bound with time, yet, there will be a rush which may prohibit you to enjoy the journey more. Also, if you are starting your Khapuche lake trekking from Kathmandu, additional 2 spare days may be required in order to cope with flight or road-way trip between Kathmandu and Pokhara.