As quoted by SB Nation: "Sources at multiple schools in consideration for Big 12 membership have told SB Nation that the window for evaluation is between 60 and 90 days."

http://www.sbnation.com/college-football/2016/7/25/12263006/houston-big-12-expansion-conference-realignment

The article is otherwise all about Houston being ready to crack kneecaps to get into the Big 12. At least that's how I interpreted they'd "do whatever they have to."