There are no clocks in Las Vegas gambling casinos. It increases the sense of freedom, a disconnect from reality and thus, increases the dollars spent gambling.
Some other tricks casinos use:
1) There are no windows, so people don't know if it's day or night outside.
2) They design casinos to be like mazes so you can't find your way out.
3) They give free alcohol to the gamblers so they continue to gamble.