Timing of my animation

My aim is to produce an animation which is a minute or so in length, but I have been advised to make it a bit longer, so that there is more to look at so I am going to add a few more seconds to it. Currently based on a test I produced I am on target, because a few of my scenes add up together to make 30 seconds and I still have many other scenes left to develop, I would say that my animation should be near 2 mins long.