The Jerusalem District Court Thursday gave the Shabak security service a 6 p.m., local time, deadline to let Hounam talk to his attorney, Avigdor Feldman.
The Shabak arrested Hounam Wednesday evening, banned him from seeing a lawyer and won a court gag order.
Hounam was the Sunday Times journalist who published an account of Israel's top-secret nuclear program in 1986. The story was based on interviews with Vanunu, a former technician at the Dimona reactor.
Vanunu was released April 21 after serving 17 1/2 years in prison.
Israel denied Hounam's request to meet Vanunu and warned Vanunu not to talk about his work in Dimona.
Hounam has been in Israel for more than a month working on a documentary for the British Broadcasting Corp.
Asked if Vanunu was using Hounam, Yaron said, "I think it was the other way around."