By Jessi Hempel
October 2, 2012

FORTUNE — Yahoo’s former CEO has a bit of advice for new CEO Marissa Mayer. Says Carol Bartz, “I’d tell her changing culture is not a sprint. It’s a marathon.”

Speaking Tuesday at The Fortune Most Powerful Women Summit in Laguna Niguel, Bartz was candid about her time at the Internet giant, saying that while she got to know the board members, she didn’t invest enough time in understanding their relationships with each other.

“How would you have been able to do that. Maybe on the golf course?” Fortune editor-at-large Pattie Sellers asked.

Bartz shrugged. “Well, that would take five hours,” she joked, before explaining it is challenging for a new CEO walk into an entrenched culture and make change. “You have to understand how a board acts as a unit. You are walking into a group of people who have experiences together you didn’t experience with them.”

Bartz is on the other side of the fence now. As the lead director at Cisco, she has learned a lot about what makes a good board. Says Bartz: “That board doesn’t panic. We consult with each other. We very much know the team. Even though the products are complicated, we work together. And we have educators, former CEOs, and technologists.”

So would Bartz jump into the CEO spot again? Says the ever candid executive: “I grew up in small town Wisconsin. I never thought I’d have bling–that I bought myself. I’m not really a planner. I’m an opportunist. If the right thing happens, I hope I’m smart enough to do it.”

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