Gambling is the number one thing in Las Vegas. Though it is not the only thing to do in vegas.
During the day in Vegas there are a variety of sites to see like the museums, art galleries, antique shopping, aquariums, clothes shopping, fun rides and more than I plan on typing out.
There are also things to do at night such as the night tours, nightclubbing, as well as sites that more beautiful to see at night when light up such as the bellagio fountains and so much more.
Regardless of whether it is day or night in Las Vegas there is ALWAYS something to. Which is one of the reason it is titled the city that never sleeps.
Gambling is available of course day and night that is something that never changes.