In a nutshell, yes, but there are all sorts of other calculations that go on behund the scenes as well, depwnding on who else has voted, and their voting strength. You also only yet rewarded for curation in STEEM POWER, which is more expensive then SBD. You may find your reward somewhere around 0.001SP. But if you vote at 30 minutes it may be 0.004SP. There are lots of other calculations to make, but the 30 minute mark is where you get the best curation return.