Well, they do not have to take two votes before Noon.
They are "permitted" two votes before Noon, right?
I mean, what if the second vote yielded no winner,
but the third did? Do they burn the second ballots
and send up black smoke, then follow it with white
smoke on the third, or just burn the second ballots
with the third and let both burn white?
Let both burn white.
From what I've heard on EWTN, here is how it works.
Two votes in the morning.
Two votes in the evening.
If the Pontiff is elected in the first ballot (morning or evening) then the result is announced right away (which means that we are now on the third ballot of the conclave, second of the day). If the Pontiff is elected on the second ballot (morning or evening) then both groups of ballots are burned white.
If no Pontiff is elected on both ballots of any one voting period, they burn black.
Did you see the Jimmy Kimmel show last night? They claim to have a hiden camera in the Conclave, even call it the Conclave Cam.
They kept going back to it during the show; the first time they showed it, the Cardinals were doing "rock, scissors, paper" to pick the new pope; the last time, it showed the Cardinals doing potato sack races.