Drive as if to the airpost and the IKTEO is on the left before the roundabout almost opposite the military base. We did not need an appointment, were taken immediately and the whole thing took a total of twenty minutes. The people were incredibly nice. There were coffee and soft drinks vending and free internet access.
The basic cost (from memory so don't assume absolute accuracy) was around 40Euros for the test and a further 20 for the penalty. I would advise going on the day or the day before depending on how it falls. Their website is at http://kteo-hania.blogspot.com/
We were advised against the one at the Mournies junction by Greeks, but Philippos obviously had a good experience.