Regarding questions about "just how close you can get to the intrinsic moral evil of torture without crossing the line," Mark Shea endorses Zippy's maxim,
To merely pose the question is to already have assented at least in part to torture, to abortion, to adultery.
I'm not entirely sure the question itself is immoral, as Zippy asserts, but I'm pretty sure it's ill-posed.
To ask, "How long can we make a prisoner stand before it becomes 'torture'?," is to pose a kind of sorites paradox, akin to the old, "How many grains of wheat can we place on the floor before it becomes 'a heap'?" There's no way to answer that question; what separates acts of torture from acts that are not torture is not an infinitesimally thin line. There is no number T such that forced standing for T seconds is not torture and forced standing for T+1 seconds is torture. The question asks to define something that doesn't exist.
Let me repeat that: Questions of the form, "How long can a behavior be engaged in before it becomes torture?" have no answer. It's not just that we don't know the answer, or can't determine it, or disagree on what the answer is. It's that there is no answer. It's a nonsensical question, like, "Does blue weigh more than middle C?"
The problem is that the question also asks to define something that is needed. If we all agree it is immoral to force someone to stand for fifty straight hours, and if we all agree it is absurd to suggest it is immoral to force someone to stand for fifty straight seconds, and if we want to proscribe immoral treatment without being absurd, then we need a way to proscribe standing for fifty hours without proscribing standing for fifty seconds.
It's bad, you know, when you need something that doesn't exist.
Fortunately, in this case the need is only illusionary. We don't need laws of the form, "More than X amount of Y is illegal"; that's simply the form we've become accustomed to thinking in terms of.
Rather, as Mark suggests, we need laws that encompass virtue:
The moment we go from framing the question in terms of trying to bargain our way out of damnation and instead frame it in terms of seeking virtue, all the fog disappears. We no longer have to wonder just how close to hypothermia we can push our victim, nor how man hours they should be forced to sit in their own feces, nor if leading them on a leash crosses the line into torture. We are trying to be humane, not trying to get away with inhumanity. And you don't do that kind of stuff to people you are trying to treat humanely.
True, that means we need virtuous judges to interpret the laws. But if we don't have virtuous judges, all the laws in the world won't make our justice just.