I think 5 minutes is generally more than enough for any cycling video for public consumption (And one side of A4 enough for any ride report....just my view).
I got 10 days of my PBP ride into 5 minutes and tried to mix the shots up a bit, to tell a story.
10 Days in 5 minutes <<<
Whether it works or not is personal preference but I made it based on the video of my son's ride (see above) video which I loved.
It was my first real go, and it's difficult to decide what to leave out, therefore having a short backing track, and editing to the beat, gives you a clear goal.
I find that having an end video in mind helps you look for shots during the ride, Cafe stops, other people, local landmarks, various angles....etc.
Otherwise it can tend to look like accident-cam footage.