How much coffee should you drink in the morning and then consider a cup in the afternoon to have a quiet yet productive and solid day

How is it possible to have coffee at just the right time everyday. Most people will tell you that a cup of Joe in the morning is critical for functioning the rest of the day. 

Also those that work in offices know about the 3 o'clock (afternoon) brick wall. From what I've understood a nap around then ( is critical) for the continued normal functioning of the rest of the day. And then that critical second cup of Joe