studies have shown that significant disruptions of the day-night cycle induce stress for most tropical fish. (i wish i could remember exactly where i read that...) my suspicion is that while prolonged light exposure interferes with resting habits, prolonged periods of near or total darkness is simply too different from everyday living. plus, sitting in a basement in the dark is pretty different from sitting around outside in a hard rain. we've had some fairly rotten weather lately in AL, but its rarely any darker than the "blue moonlight" systems most people run--which is to say, totally different from the actual dark. (PS, the detrimental effects of constant light are another reason i feel that 24-hour Walmarts should not carry fish.)
while a constant twilight (indirect or diffuse lighting) would be preferable to leaving fish in complete dark or light for several days, the best thing to do would just be to attach a light timer to the tanks. for temporary installations, a single timer can be attached to extension cords running to each tank, but i actually find using timers to be quite convenient on an everyday basis.
but i agree totally on the food thing.