The time to transport a car to Hawaii very much depends on your exact pick-up and delivery locations. From the Midwest (Chicago for example) to any of the ports on the west coast, takes about 5 to 7 days to deliver the vehicle. This excludes the pick-up time frame which is usually from 1 to 5 business days. Then from the port a ship leaves to Hawaii every week, and it takes about ten days to deliver the vehicle by water to any of the islands in Hawaii.
From the time the ship leaves the port you can count 10 days, but keep in mind that this is the open ocean and weather can delay transportation. The same applies to the ground transportation within continental US.
The transit time to Oahu is 10 days and 17 days to Kauai and Maui. One or two days before your vehicle arrives at the port in Hawaii, a representative will contact you to let you know of the exact day and time you can come pick up your car.