“I would have said about an hour, an hour-and-a-half, to be about the maximum. A lot of people do say when they come out of the cinema that they are aware they’ve done something different with their eyes, even if it’s not to the extent of a headache or sickness, but they’re aware that it was hard work to watch. I’d have said that was more than enough.“I’d would worry about people spending hours doing it, I must say.” – James Sutton, eye specialist and MD of British eye health company Butterflies Healthcare

Thats not to bad at all. With my ADD I am lucky to even get to the hour and a half mark.