Yes, it took about that time in total to remove the head and re-fit the new HKS gasket (this does not allow for time to say have the head checked for straightness and other jobs I did at the same time).
I guess the disconnection of the turbos took about 2 hours. So for the complete job, inluding time to re-fit the turbos, would be 8 hours.
I really think that it looks a daunting job, but its only nuts and bolts. The trick is not to get scared!
Nik