Is the sun from 4pm to 5pm harsh?

rising sun and setting helps skin synthesize make vitamind which is good to process your low density lipid (fat)

Well yes but nothing compared to the mid day hours. Remember as long as the sun is up it is always going to be really harsh outside. If you want to prevent tanning or burning just wear a the highest SPF I wear a 100 it protects from 96% of uv rays and apply every two hours I apply once a day, I think it will take too much worrying if I applied every two hours.