Yes, that's correct. If you're trying to maximize your curation rewards, you have to weigh the risk against the reward. The longer you wait, the more likely it is that votes are going to come in before yours. Yet if you vote too early, any reward you would have received is going to be greatly reduced. For the most part, voting in the first 5 minutes won't earn you much. After that, it's a guessing game. There is an element of luck to it.