Hey!
Good question. Personally, I think it depends on the type of video. Let's say you're a vlogger: people will expect longer videos because they want to find out more about you, what you get up to in your day etc, but if you're channel is based around gaming, it's not recommended to upload a 30 minute episode of a Let's Play. Take that episode and split it into 5 parts, that's 6 minutes per episode, and if people enjoy the series, they will keep coming back, as 6 minutes is much less than 30 and people can find time to watch that video!
Hope that helps!