I just need to set the date temporarily. I run this

date 051918002010.00

and it sticks for just 5 seconds or so. Then it syncs with the time server. I have tried:

ps aux | grep ntp

but there is nothing there.

I need a correct answer now, more than a more detailed answer later :)

Edit: As answerers quickly discovered, my Ubuntu is running in a VirtualBox, which turned out to be relevant for some versions of the answer. Thanks to everybody.