Any studies concluding a corelation between being awake at night and poor health are likely measuring many confounding factors. There's no way to isolate that variable. Certain groups are more likely to stay up into the night, which could equally be the cause. It also requires, as the post implies, giving up certain activities. Those activities may promote good health in some way.

Any actual medical condition caused by nighttime activity could be managed, like vitamin D deficiency. The societal factors can't be, although if it was more common and acceptable that could level out some of the variables.

No worries, I take Vitamin D pills. I have surpassed my sun-addicted brethren.

Studies show that losing weight is good for your health. What happens if you give that advice to someone who's underweight?

Different people have different needs and the studies on sleeping haven't yet caught up to that level of science.