What is the healthiest time of day to drink coffee?

Probably morning.... Depends on what you mean by healthy. If you are drinking caffeinated coffee, drinking it earlier in the day is less likely to cause you problems falling asleep at night, especially if you are sensitive to caffeine. Some people will have problems falling asleep at night if they consume coffee after 12 pm. Otherwise, if caffeine really doesn't cause you these problems, anytime is fine for coffee.