The post is open for seven days. The value of the post during that time can fluctuate it seems due to market demand. The most opprtune time to upvote is 5 minutes after posting. In your wallet you have 3 types of currency: Hive, Hive Power and Hive dollar. The Hive Power is like your gas tank. That's where your vote comes from. No matter how much you vote you won't lose it. Just takes time to recharge. Like 2 hours. Try and app like PeakD and you can see percent values of voting power. After seven days the post is closed for voting and a percent is returned to the person who whote and to the voter. Please do some research and read the white paper.