The upvote percentage does not make a difference in earnings - you just will get rewards proportional to your upvote. You don't have to vote posts early either - ideally you need to vote before the big votes come in on a post - so you can vote on older posts with few rewards that you know are good - and then share them around and try to get bigger votes after you to earn. Or you vote in 3 to 5 minutes on authors you know get high rewards - trying to get your vote in before the big ones arrive so you get the extra curation rewards.