Someone asked this on another thread--I'd look for it, but the answer was short: "Yes, if you get on the earliest plane, take a cab to the Brazil side, do an aerobic walk not taking any pictures, skip lunch, jog around the Argentinian side, and take the last flight back to BA." I think the response was a little "toungue in cheek."

I spent two nights last summer while traveling with a friend and we both agreed it could be easily and enjoyably done staying one night, although we were glad we had the luxury of staying two:

Take an early flight out and try to arrive at the Brazilian side shortly after noon. You'll have a few hours before the park closes.

Stay at the Sheraton, if you can afford it, but you could stay elsewhere in Puerto Igauzu and still be okay. Take a cab so that you can be at the falls as soon as the park opens. If you're in reasonably good shape, you could walk all the trails and have time to stop and enjoy some of the incredible vistas. I found that I walked the trails in half the time posted on the signs at the beginning of each and I wasn't hurrying at all.

Take a cab back to the airport for the last flight out which was around three when we were there in June (off-season), but there may be later flights in peak season making a one-night trip more feasible.

You won't have time to take the boatride up to the falls, but when we were there, they weren't running the boats because the damn below the falls had been opened the night before and the water level was low. The drought was not a factor.

If you think you'll get back to Argentina, I would wait until you can spend at least one night. If this is a "once in a lifetime" trip, I think you should go for it, but only if there is a late afternoon/early evening return flight. It's one of the most spectacular sights I have ever seen, but you definitely want to see "Devil's Throat" from both sides.