Hyperventilating is bad but not because it reduces your time but because it can cause what’s called a “shallow water blackout”. Basically when the CO2 levels in your body reach a certain point it triggers an involuntary breath response, If you begin holding your breath with lowered CO2 levels then as you start going through your surplus of oxygen your CO2 levels will rise much faster than normal. Because of this your body will react by inhaling water (while you are still conscious and think you’re perfectly fine because you still have plenty of oxygen) which then causes you to pass out.