A little science is in order for such a speculative title.
Let’s start with the rumor that Quinton Jackson and Lyoto Machida will be the two coaches for The Ultimate Fighter 10. There is enough secondary evidence out there to suggest it will in fact happen.
Based on that reality, it is worth speculating when a light heavyweight title fight will happen between the two. In order to more accurately predict that, you must look at the most recent time line for the TUF 9 season.
"The Ultimate Fighter 9: U.S. vs. U.K." debuted Apr 01, 2009. The Finale is scheduled for Jun 20. That is a difference of 11.5 weeks. The debut shows fall on a Wednesday and the finale shows fall on a Saturday thus accounting for the half week.
The two coaches, Dan Henderson and Michael Bisping, will fight exactly three weeks later at UFC 100 which goes down July 11.
Just to gather more data, to support the case, let’s look at the TUF 8 time line.
The Ultimate Fighter 8 Debut aired Sep 17, 2008. The finale aired Dec 13. The time difference for that season: 12.5 weeks.
The two coaches, Frank Mir and Antonio Nogueira, fought at UFC 92: The Ultimate 2008 on Dec 27, 2008. The gap between the finale was exactly two weeks.
Going back to TUF 10, we know it is set to debut September 9.
It may be more appropriate to follow the TUF 8 time line given they are during similar times of the year.
If you add 12.5 weeks to September 9, we get a date of December 5.
Based on the evidence, if in fact Machida and Jackson are the TUF 10 coaches, their title fight will happen December 26 at UFC 106: The Ultimate 2009.