I did it about 10 days ago. I actually started next door to Irun in Hondarribia. According to my Garmin GPS watch, it was just under 25 km. There was 1,060 meters of ascent and 1,044 of descent, on the high ridge alternative. Some of the terrain is steep and rugged. It is likely drier now, but there were some muddy sections that required care to avoid wet feet.
With breaks for a couple of meals, photos (views are spectacular), etc it took me 8 hours elapsed. According to the watch, I was actually moving for 5 hours of that. My average moving speed on the flat with full pack is 5.5 kph, but with all the up-and-down I could only manage 5.0 kph on this section.