They took about 45 minutes to assemble 4 of them.  I used a cordless drill with hex and crosspoint screwdriver bits.  I have adjustable torque/clutch on the and that keeps you from over tightening/stripping out the screws. Do not use a power screwdriver without that!.    They assembled quickly once I put one together to see the sequence.
They are very nice chairs and the blue finish matches the rest of our beach themed  dining room.  The attachment screws for the seats are not predrilled so you will need a power driver or use a 1/16" drill bit to predrill the holes if you plan to screw them together by hand. 
We love the fit and finish and they are a great value for the money ($151 for 4)!  We plan to get 4 more when the price drops again.