Kinda. Your curators get the most if they wait till after 30 minutes to upvote you. If they upvote before 30 minutes, you get more of their vote and they get less. So if you want to maximize the curation reward your followers get, you should wait some time after 30 minutes to buy the votes.

There's a little more going into it with curator vote ordering and vote weight, but that's a little over my head. Just remember that if you're buying votes past the 30 minute mark, you're buying income for your curators and likely taking a loss on the vote yourself. If that isn't something you want to do, you should try to buy votes as soon as you can.

Of course, if you have less than a few thousand STEEM none of this really matters. Just focus on putting out content!