TDT's calendar is only his best guesstimate based on what he has to go on with length of season, number of castaways, start date, end dates, precedent of last season.

Last season he did not believe there would be truels until it happened, and then he changed it up.

TDT does GREAT calendar, but it is not based on special sourced info AFAIK.

The current teaser says Double Eviction rather than Two Tribal Councils, so I expect it is all one evening.

I don't know how they will handle the duel, but let's take a look at the numbers:

12 people made merge, and there will be 5 in the "in camp" game as of Ep 14.
There are 12 in the game as of Ep 9. Assuming no duel, Eps 10-14, 5 episodes, eliminate 7 people from the game. That means there have to be two episodes where 2 people lose at RI.

One should be Ep 10 -- 2 of 3 (Keith and the 2 Ep 9 boots) go to Ponderosa.
Ep 11 -- one goes
Ep 12 -- one goes
Ep 13 -- one goes, double tribal. 2 voted out.
Ep 14 -- 3 way, 2 are out.

Well, here's an idea of how to avoid a truel: next time they have a duel at RI, have Keith battle the first boot, and have back to back duels where the victor immediately battles the second evictee from Ep 9.

Or they have a duel in Ep 9 by having an early TC, but that's hard for me to imagine.