Trigger based events or Timer based events?

So I am at the part of the project where I need to make things happen, sounds playing and/or objects animating, without user input. I know I could do these if I had the user trigger something, however the user will be sitting in a chair and not moving (short of the headset).

Are there any other options besides user activated Triggers or Timer based? I am thinking my only option would be Timer based at this point but also do not want the events to be mundane after playing it awhile.