Awesome day hike. I learned that you can either reserve your own permit 2 weeks in advance or go on short notice with a guide. My lodge (Chiang Dao Nest - which I highly recommend) was able to arrange it for me the afternoon before. As an experienced climber and hiker, I was chuckling to have one guide in front of me and one behind the entire way - like I was a baby elephant. :-) It's a tough hike - 11 miles 3500ft gain, but nothing you can't handle if you are a regular hiker. So ignore the locals protestations that it is too difficult and dangerous to do in one day as I think the Thai, while active, are not super adventurous people. It was also surprisingly cold on top for me and clouds obstructed my views, but I said "mai pen lai" as the Thai do ("whatever may be"). :-)
Superb dayhike and loved the views of the surrounding peaks and cliffs. Pretty cold on top, the only downside is the views were a bit tarnished by smoke from the surrounding areas. But would love to go back sometime.