You will have to get above the treshold before the end of the payout period...past that, people can't vote on an article. (as the rule stands right now and it may change in the future).
Each post are independent. If I don't get votes up to the amount necessary, no DoFollow on the article. This is why investing in SP can have SEO benefits.
Thank you for this explanation. I will have to grow my sp organically as I have nothing to invest but I will focus on doing that :)