Definitely go at NIGHT. You get to the top of the tower and see all the lights of Vegas below you. The view is very pretty, and it's nice for the people who don't want the thrill of the ride.
You have probably been on rides like this one before that shoot you up and let you free fall down. The twist of this is that it's happening on top of a building.
The initial shoot-off is with amazing force. You really feel like you have just blasted off to the moon. When you get to the top, there are a few seconds when you feel you are floating over the city of Vegas, and then you go screaming down again.
What a rush!