I do believe "advancing your PC clock to force instant growth" is something that the admins on this site consider to be a form of cheating.
It's certainly not something they'd recommend. I don't think it's quite so bad for PT, but certainly advancing the system clock in Virtual Villagers can have all sorts of unexpected and unpleasant effects; even worse is setting the clock back. In addition, changing the clock can confuse other applications running on the system.
See the FAQ at
http://www.ldw.com/support/faq.php?game=5&platform=9&f=59&q=519#answer