Personally I wouldn't watch any videos that doesn't have English audio. I'm thinking this will be true for most non Portuguese speakers here but I can't speak for them of course. 30-60 minutes is good length. Just make sure you cut it off at natural points in the video. I used to do 60 minute videos but cut it down to 30-40 minutes as it felt more natural.
I say just go for it and see how it goes. Worst that happens is that it doesn't catch on.