When timing is 180 degrees off of where it should be it causes the plugs to fire when the cylinder is not going through compression. So instead of firing when it should it fires to earlier or too late most time not igniting any fuel making the engine not run.
One hundred eighty degrees is a very high temperate outside. It is not a typical weather outside so companies do not test their vehicle that high of temperature.
Because your crank turns 2 turns to 1 cam turn. So if you are off 180 then your valves may still be open and your spark plugs will fire on the wrong stroke (the begining of the intake stroke instead of power stroke)