I don't think anyone can answer your question.
If you cut your margins on reducing time to get a flight you take a risk (as in life) You should be prepared to miss your flight as worst case scenario. How important is your destination or the reason for your flight? Cut it too fine and you miss your flight, waste money and you should not be disappointed. How much of a risk taker are you? Go early, take a travel neck pillow and you can power nap at the gate. At least someone might give you a shake to board the plane.
It is a bit like going out on a winters night in a warm car and taking nothing at all with you other than the clothes you stand up in. Plus impractical shoes? No coat, no phone and then you break down. Your phone is about to die but you have no means to charge it. All very foreseeable events with a greater or lesser probability of occurring. But the consequences?
If you cut margins you take a risk. No one can quantify your individual risk. You have to decide how close to the wire you are prepared to go. What if you lose your keys when you are about to set off - you oversleep or wake up in a half cut state? What is your margin if your car has a flat battery, or that you have mishaps on route? That you have insufficient fuel, that there are road closures or night diversions? That you can't get safely parked at the airport or the shuttle bus is late? What if the hold ups to get through check in and security are unusually large? Do you have time to turn back if you have forgotten your passport?
I would like to say if all else fails get the train but .....
Anyone would think Scotland was a different continent?
Most things in life are survivable. The fallout just gets more expensive according to the damage left behind.