According to this article in Science, Psychologist Emese Nagy has noticed that all hugs that occurred at the Olympics lasted about 3 seconds. Then he noticed many other things that took three seconds. It seems that our feeling of "nowness" lasts about three seconds:

Crosscultural studies dating back to 1911 have shown that people tend to operate in 3-second bursts. Goodbye waves, musical phrases, and infants' bouts of babbling and gesturing all last about 3 seconds. Many basic physiological events, such as relaxed breathing and certain nervous system functions do, too. And several other species of mammals and birds follow the general rule in their body-movement patterns. A 1994 study of giraffes, okapis, roe deer, raccoons, pandas, and kangaroos living in zoos, for example, found that although the duration of the animals' every move, from chewing to defecating, varied considerably, the average was, you guessed it, 3 seconds. "What we have is very broad research showing that we experience the world in about these 3-second time frames," says developmental psychologist Emese Nagy of the University of Dundee in the United Kingdom.