yes upvoting early brings curation rewards.....infact earlier votes get maximum curation reward but it also reduces the value of total reward pool if your vote is worth alot like 10$ andyou vote on first min only then almost 99% of your 10$ vote will go into author reward that is almost 9.9 for autor and 0.1 for curator but if overall earning of the post is now 100$ frm whic total 20$ is going into curation then as your vote was earliest you will receive maximum curation reward like you will receive almost 18-19steempower.......but if the post overall make only 12$ after your 10$ vote then total curation will be only 0.1-0.5$ and what you will receive will also be low