Negotiations for potential buyers of Chase Field had been scheduled to end Oct. 31.
The supervisors agreed Monday to delay the deadline to afford groups more time to possibly get a deal done.
The county owns the stadium and the Diamondbacks argue that it needs $187 million in repairs.
County officials want to avoid mounting repair costs they believe taxpayers cannot or should not be required to pay.
The stadium opened in 1998 and county taxpayers spent about $250 million to build it.
Supervisors have set a starting sale price at $60 million, but promise to get at least fair market value.