Friend [object-を] choose time [topic-は] no-matter-how careful-even overdoing [topic-は] is-not.
どんなに~ても~すぎることはない is a variant of the いくら~しすぎることはない pattern — 'no matter how much you X, you cannot overdo it.' どんなに and いくら are interchangeable here. A proverbial construction often used for advice.