Hello Mara:
Yes, that is a challenge! I am wondering about this one hour time you have stated...is that all the time you have to do the painting? I am assuming not...
So I will recommend to you a combination of photos and life work for this.
Have them get you a good spot, close to the action. Set up before the show and take pictures of the stage and background in the light so you can understand the details you will be seeing later.
When it gets dark, have power available and a reasonable lamp for your canvas that you will clip on. Have your camera at the ready as well.
Mix up as much of a palette as you can for the situation you will be facing. Painting such a scene will be a bit of a jumble as you will have objects in dark which will be low chroma, and objects lit by stage lighting which will be high chroma..colored lights will make this more complex too.
Rock stars are not stationary objects that hold a pose while you paint away. You don't have time to take pics and paint, so get a friend who understands photography to snap away as the action goes on for the hour, and pray pray pray that you get a shot of your rockstar that you can use for the final painting.
Meanwhile, you are sketching, painting, or whatever you need to do to capture the "essence, atmosphere, and feeling" of the scene - instruments, glare, lights and shafts of light, etc.
I would ask for a sitting with the musician as well, or at least some close up photos that you can use for reference.
In the end, you are going to end up with a composite painting from multiple sources and reference. I cannot see any other way to pull something like this off.
Hope that helps!
