I was startled at the number of pilots on this thread who were clearly a bit surprised when 18Wheeler mentioned it takes about 20 seconds to shut the engine down after pulling the fire handle. Right there is good enough reason to at least push it back sometime, in the simulator, without it being part of an evolution, surely?
It's the way they're made to work on the 747 Classic. The one in question was a GE CF6-50 powered contraption, (with the reversed wiring being done at a certain Chinese maintenance company, not the company I flew for) and the reason it took so long is because they are really intended to be used in-flight, where the fuel-flow is far higher and so they will run out of fuel much faster than they would at idle. As mentioned in another post, other aeroplanes have slightly different systems, such as the 777 which has another shutoff valve closer to the engine so it shuts down much faster - the negative side of that is that the fuel line from the wing down to the engine still has fuel in it.