Actually, your steem power recharges in real time. That's the reason @lottobot only does a vote once every 2.5 hours, because that's the amount of time it takes for a single 100% upvote to recharge. You can check out lottobot's page on steemd (here: https://steemd.com/@lottobot) to see how much voting power it has at any given time. You'll find it recharges back to 100% by the time each lottery winner is chosen :)