Ok, and I do that for the most part. It's just the idea of "scheduling" a talk that never works with her. It's either then or never. The only way I have found to semi-schedule the talks we have is to just bring it up at a "good" time (as you suggested) or just refuse to carry on the conversation until a better time comes along.
As for Mars/Venus, it is a cornerstone in my efforts to save my marriage. After DB/DR and along side 5 Love Languages, it has been invaluable to me. I LOVE that book.