SS - so you're 2 miles from the base, daytime, weather's fine. You've just hit 70kg to go, and you know you can be on the ground in 2 minutes. You also know your red low fuel warning light has not yet come on, which it should at 60kg, when the book says you must land within another 8 minutes. Are you really going to park it in that muddy field - or continue land with the 64kg you've worked out? How about you SAS?
Course I'm not saying it's right to be in that situation, but I think the reality is you have a bit of flexibility according to the circumstances. If you're cruising along at FL80 you'll be making that landing decision a lot sooner, given that it will take you say 5 minutes and 10kg of fuel to get on the ground.