Yes, there is a penalty in the first 30 minutes that goes from 100% to 0% penalty. There is no "right" time to vote, but if you vote immediately after the post is created, you will get almost no curation reward. The tricky part is, if you wait until the 30 minutes is up, the opportunity for curation reward is usually mostly gone as well, as high reputation users will have already gotten to it. It's a complex problem, with no straight answer in terms of the right time to always vote