From the SMH:

Some youngsters are spending hours at night on email with their friends. One fad is “the 30 minute rule,” in which a child who doesn’t respond to email within half an hour gets targeted and picked on by other schoolmates.

In Japan, people don’t use computers like we do, they do all their chatting on their mobiles via complex email messages. So where the computer has replaced the TV as the family addiction in other countries, it’s the mobile phone in Japan.