These four events repeat every 'tropical' year (365 days, 5 hours, 49 minutes), so they become later by about six hours, or (if there has been an intervening leap day) earlier by about 18 hours, from one year to the next.
The three distinctive signs and symptoms of autism include problems with verbal and nonverbal communication, difficulties with social interaction, and repetitive behaviors or narrow, obsessive interests. There are three distinctive symptoms of autism.
Symptoms of autism typically appears during the first three years of life. Some children show signs from birth. Others seem to develop normally at first, only to slip suddenly into symptoms when they are 18 to 36 months old.