I went on the neon museum website on the day that I wanted to go and there were three spots (for two people each) left at 10am on a Sunday. They were for 2:30, 3:30 and 5:30pm. I hear that nighttime tours are better? But it wasn't meant to be!
I bought the ticket that's for students [$15] and once you get to the neon museum front desk, the employees check your student ID.
The tour lasted about an hour. I thought it was informative. I learned about the $$ of signs and the history of Las Vegas.
It's great that they have benches every couple of yards or so, so if you have any mobility issues, you can pop a seat wherever and listen to the tour guide.
I got some great photos of the gigantic signs. I would definitely encourage others to check it out!