Las Vegas local here saying this is hands down the best and most authentic Thai food in Vegas. Not in the best side of town and a bit tricky to find, but don't let that deter you. It's worth the drive and wait. Usually busy and that's always a great indication the food is going to be good. Fellow foodies know what I'm talking about. If it's good enough for Anthony Bourdain, it's good enough for me.
My go-to's are the Garlic Prawns and Tom Yum Shrimp Soup (level 9) because i like it hot :) Crab Fried Rice and Northern Larb. My kids love the Chicken Sa-tay with peanut sauce.
Again, it's gonna be busy no matter what time you show up, just know they take reservations and usually the wait isn't too long. Plenty of parking too.