Start now. This is what we do to ourselves generally speaking. We set an arbitrary date and the day comes and goes with a new excuse. Why can't you make a better eating choice for lunch today? Not picking on you, just using your post as an example of a mindset that isn't committed to making a change NOW.
because me and my wife are starting an exercise program together and starting the Paleo diet and tracking it together with our chiropractor. I have already began watching what I eat but the REAL program starts Sunday morning with breakfast.