Why it is so complicated is because they have to counter auto vote bots. I don't really know why they picked 30 minutes either. I don't like the current algorithms at all. They should just give people enough time to decide what to vote on and pay them every week.
If you vote after 7 days it doesn't add rewards, it only increases the votes by 1. It's fucking stupid, all your hard work is essentially useless after 7 days.