Shorten it. Longer voting does not generate more interest imo. I think that 10 days is plenty, in this day and age, you can access the internet anywhere, so even if you're on holiday, you should still be able to vote. In fact, I think having a shorter time to vote may actually INCREASE voting: Whenever there is a buzz with a new contest, semifinal, final etc..., you want to take advantage of that buzz. Non-Gothicomp regulators (participants or voters) may move on without voting if it takes too long.
Just my 2 cents anyways.
Thanks,
CF