We went on the 6pm tour on January, and it was quite dark by then. I was a little disappointed as most of the neon aren't lit up, only a handful is. The rest has colored spotlights on them which was cool but I feel a day time tour would be more beneficial if you want to see the unlit neon in all its painted glory. I love sign painting but at night you can't really see the details on it very well. The actual lit neon is beautiful especially at night, but I feel we could see more neon on Fremont anyway.
However I enjoyed the tour very much, it is full of historical facts about vegas. Really cool and I learned a lot. The tour was one hour but the guide doesn't care if you drift off and look around as long as you're in his line of sight.
Overall I'd say it's a cool way to spend an hour if you're in the area. Btw it's not a very safe area so I don't recommend walking there from Fremont. Take a cab or uber. I don't know if it's worth traveling here all the way from the strip unless you're really into sign painting though, or you're into photography cos this place has great photo spots.
Oh yeah, some of the tour guides and guys at the counter is ultra hot. Love that beard ;D