1. You can vote.
2. The deadline is tomorrow.
There are other things it might be nice for you to know, such as: the Locus Awards are one of the largest (possibly the largest) sf awards going, judged by the number of people who vote; although you don’t have to be a Locus subscriber to vote, if you are and vote you get an extra issue added to your subscription; or, if you want to vote for something that’s not in the drop-down list (such as, say, Harry Potter and the Deathly Hallows, or Sharp Teeth, or The Carhullan Army) you just write it in the box to the side.
In conclusion: go vote.