Curation rewards pay out at the same time as the posts do, after 7 days. At first, when you have limited Steem Power its much harder to earn curation rewards because you get a smaller share of the rewards so you need to make the right votes for max efficiency.

@liberosist wrote a great post about voting efficiently here : https://steemit.com/curation/@liberosist/mind-your-votes-ii-a-guide-to-maximizing-your-curation-rewards