I see quite a few people who change their computer clock in an attempt to increase their food or tech points. I always advise against it, but it still happens. It's a really really bad idea. Most of the time, it messes up the game. Villagers die, tech points disappear, etc. That's all bad enough, but the thing that worries me even more is how changing the clock can mess up lots of other computer functions.
Think about all the things that rely on the computer clock. All documents are date and time stamped. System recovery is marked with dates and times. Calendar and scheduled events. Pretty much everything on the computer uses the clock in one way or another.
On top of all of that, you're missing out on the game itself when you cheat your way to more food or tech points. What's the point of playing a strategy and "real time" game if you're just going to change the clock to to "beat" the game?
So, please please please... don't change the computer clock when playing Virtual Villagers.