There is no definite number of seconds that a person might look directly into the sun and not cause permanent damage to their retina. Each of us is different, the angle of the sun, the amount of clouds, and many other variables come into play. What we can say is that staring into the sun can and does cause permanent irreparable harm to the retina of the eye. Lenses that filter UV light can help to reduce this sensitivity, but it is, by no means, sufficient to protect the eyes when looking directly into the sun. If you had sustained any real damage to your retina, I suspect you would notice a black spot in the center of your vision in one or both eyes that does not go away. I urge you to see your ophthalmologist (Eye-MD) soon if you have any noticeable effects of from sun exposure.