Which video is it and where did you access it from, as I'll try it for myself later on?

If it's the type of video I'm thinking of (the ones where you get the 'Get Reward' green button when the video finishes/after a set time, then says 'Successful' shortly after), you'd just need to wait it out, though now and then, even if it's after 30 minutes, I can usually get them after less than 10 minutes most times.