For instance, if the place I am ordering from is in the check-in area of an airport.
I would think that in this situation a moment's thought would tell you that a lot of the time, when you say "that'll take five minutes" and the customer says "okay" they are thinking "if I scarf the food down in ten minutes and estimate another fifteen or so to get through security then I should just about make it in time for boarding."
Which means. That if you tell me that my food will take five minutes. And twenty-five minutes later nothing has appeared, and I am already looking at the clock in horror. And then I go ask how long this will take and you tell me "oh, just another minute!" and another five minutes later nothing has appeared. And I am forced to then leave to rush through security because I am not going to bloody well risk missing my flight because you can't keep time, having already paid for the food that will now have to be thrown out if it ever gets done, looking forward to having my stomach start to digest itself because I am starving and due to my travelling itinerary this was pretty much my only chance to get food until dinner...
yeah, I am never ever ordering anything from you again.