The visit to the Chihuly Garden is a self paced tour so the time it takes for you to go through the Chihuly Garden entirely depends on you and how much time you spend in the galleries.
Although it takes most people 1 to 2 hours to complete the tour of the Chihuly Garden and I believe the last time I was there it took me a little less than 2 hours but expect to take 1 to 2 hours to complete your tour through the Chihuly Garden.
It's also recommended to make your reservation online.