You're going to get different advice from different people. The curation algorithm is pretty complicated so I don't truly understand it. But I'll tell you what I do. If I see a recent post by a person that usually gets a lot of upvotes, then I will do my best to be one of the first upvoters on that post. But if I see a recent post by someone that doesn't usually get a lot of upvotes, I will upvote between 20-30 minutes from when the content was originally posted. Another thing to point out is that you shouldn't upvote like crazy. That will just deplete your voting power and you're going to have to wait a few days for it to recharge.