Ok. I have a little trouble with thermo normally, but this one seems to be missing a key bit of information, doesn't it?
I tried to reverse engineer it by saying the water cooled by blackbody radiation. Assuming I have Stefan's constant memorized, and that I can do the quartic of 373 K in my head, we get the correct answer if we assume that the liter of water has a an exposed surface of of 0.1m^2--which the word "pan" doesn't seem to explicitly endorse.
There's very little out there on the actual time-dependence of thermodynamics. Most of the stuff I read talks about equilibria which is frustrating (sounds more like statics to me). I never had a stat-mech class, maybe someone who has can help?