30 minutes is a bit long for the time penalty. I think you could make it 5-10 minutes and remove the penalty for voting on your own post, as I think that is silly to impose a penalty on voting on a good article yourself.
Another option is to make it so that an increase rewards to the author of a post is in order, and a complete removal of the ability of voting for yourself. This way, you will automatically receive the rewards that you would have received by voting for yourself, without wasting Steem Power, and not have to worry about the time penalization.
I had a similar idea for my wisdom idea, forcing one to vote for themselves (invisibly) everytime they post. (But this wisdom system is quite different.)
That's already implemented. Everyone is able to vote for herself instantly. I see that is a way to rob other voters if the author does it with a big stake.