Jay Leno is going back to his 11:30 PM time slot, and it's looking like Conan O'Brien is the odd man out ... sources tell TMZ.

We've learned Jay's 10:00 PM show will go on hiatus February 1. After the Olympics, Jay will take back his 11:30 PM time slot. What has not been decided -- whether Jay's show will be a half hour, followed by Conan, or whether Jay's show will be an hour and NBC says sayonara to Mr. O'Brien.

We're told Jay and Conan have both been told of the changes. As for Jay, interestingly, he'll get what he always wanted -- his 11:30 PM time slot.