From my understanding, your vote retains its value for the first 10% of Manna. So if you have the 17 000 you could vote at $1, 5 times a day but with each vote, it does reduce the value slightly at the 3rd decimal point but not much to notice.
Once you hit your second 10% Manna bracket begins to reduce much faster
In theory, waiting the 2 or so hours would be better because you're giving that maximum vote but its too small to really notice.
Voting at lower % allows you to sort of max vote more often since the time it takes to restore manna is shorter, so you could in theory vote more times at 10% or 1% and just keep waiting for that max manna to hit before you vote.
At least thats how I see it