The plan hasn't changed – she still wants a baby. But Beyoncé Knowles says she and husband Jay-Z aren't on a specific timetable for when it might happen.

"My ambition is to continue to learn about the world and to eventually have a family," the singer-actress, who turns 29 on Sept. 4, tells You magazine, published by Britain's Mail on Sunday.

Pressed for specifics, Knowles – who was the subject of pregnancy rumors last winter – says she can offer "no dates, no times – it will happen when I am ready."

When she does have a child, it will add another major element to an already hectic life. Finding a balance amid the craziness, Knowles admits, is sometimes hard. "I love so many different things, and to have the discipline to turn certain things away and focus on one thing at a time so that I can give it 100 percent is really hard," she says.

"Probably the biggest challenge in my life is time – making sure I have time to be a wife, to be a singer, to be a songwriter, to be an actor and still have time for my clothing line and now for my perfume [Heat]."

But she gets by – usually with a little help from her girlfriends.

"I love being a woman and I love being a friend to other women," she says. "I think we learn a lot from our female friends – female friendship is very, very important. It's good to support each other, and I do try to put that message in my music."