You can publish short videos as well as long videos on youtbe. What kind of videos will earn you more money? Well, watch time, or the total minutes viewers spend on your videos, is the secret of making money on youtube. Therefore, longer videos can help you earn better as long as your content is engaging and makes people stay longer. When people watch your videos, it will be pushed to prime spots like the home page and suggested video lists. More watch time not only means increased visibility but also more ad impressions, translating into higher earnings.