You'd better have the eye exam in the morning because your eye pressure then is stable then. You should make the eye exam at your casual state. Thus the result will be exact. If you want to buy the eyeglasses, you'd better have the eye exam to check the exact prescription. Or else, higher or lower prescription of eyeglasses will not be good for the vision.
Well, it is hard to say when the best time to have an eye exam is. Generally speaking, the best time of the day for an eye exam depends on the time when you are most alert. For example, if you like waking up early, the eye exam in the morning would be better, for if you have an examination at the end of a day, you may be very tired and your responses during the refraction may be difficult. So you may be supposed to go and have an eye exam in the morning of day.
Generally, it shouldn't make a difference what time of day your eyes are examined.However,according to the regular conduct and experience, the time varies because of different ages.For young children, the morning of the day or after a nap when they have a rest.During this time,they are willing to get an exam.For adults,you just come to get an exam as long as you are in good health and feel vigorous.That is because having a good health,means your eyes are also in goo d health.For seniors,the morning of the day will be the best time,that's because seniors always get up early,and they are in good health and feel sober in the morning.Under this condition,getting an eye exam must be successful. As i don't know what your age,you choose for yourself.I hope i can help you sincerely!