This sounds like a question the Car Talk guys would call bo-gus!
The question is - at what point after brewing does coffee have negative effects worse for your body than when it was first brewed. That suggests coffee has negative effects when it is first brewed.
What are the negative effects of freshly brewed coffee? Aside from bad taste of cheap coffee? A lot depends on the condition of the person drinking it. There is a lot of small print. OK - not counting the effects of boiling hot coffee poured on laps of people exiting drive-up windows. Not counting people who have over-caffeinated. Not counting people with heart problems, pace makers, pregnant women, and the usual roller coaster disclaimers. OK and let's not count people who drown in the stuff -or who, like guy who doesn't know how to the proper technique for eating a pretzel, chokes on it.
At what point does coffee become bad for "normal" people under "normal" conditions?
You've got issues with oxygen contamination - but that just makes it stale and eventually bitter. High grown arabicas hold up better.
You've got contamination issues to deal with - that depends on the environment and how clean the container was before coffee was put in.
Coffee is an astringent, so you're not going to get a lot of things growing in it for a while. But that eventually happens.
Based on coffee cup experiments over vacation, I think when little blue islands start floating on top is when there might be negative effects. Granted, I've never consumed coffee with little blue islands floating on it, but it does happen. So I'd say within 1-2 weeks (more/less depending on contaminants, environment, humidity, temperature, etc.) there is a high potential of negative effects.
But if you drink coffee for the coffee instead of for the great cause of science, you want to drink it within 20 minutes of brewing, especially if it is on a heat source like a burner. If it is in a pre-heated airpot or Thermos, you can get a good 60-90 minutes out of it. Less if you start drinking it - because you get cold air coming in.
If you toddy brew good coffee (high grown arabicas) and store it cold, you can get much more time.
This year, the Ig-nobel prize was awarded to a woman who validated the 5 second rule
http://www-tech.mit.edu/V124/N41/41_ignobels.41n.html
Maybe next year, you can try for an Ig-nobel prize of your own on this subject.