Analysis of viewing figures shows peak demand for FilmOn's "naughty movies" was around 1116 GMT on Sunday.
In stark contrast, internet analysts Hitwise found that usage of video sites peaked on Sundays but more traditional adult sites experienced a dip.
It stated that Sundays was the top day for visits to internet shopping and social networking sites, reports the BBC.
Explaining the film viewing data, Alki David, founder of FilmOn, said: "The data applies to both men and women and it certainly poses the question about what has happened to the traditional 'day of rest' in Great Britain."
David, however, is unsure why adult content was favoured.
"I have no idea. It may have to do with the Winter and the oncoming depression. Cheap entertainment seems to be faring quite well right now, and adult content is the most extreme distraction of all," he said.
Different genres of downloaded videos peaked on different days; "family viewing" films experienced a peak on Wednesdays, while sport-related titles showed a Saturday spike in sales.