Pretty sure the timing is the same.
Yes 50 is the max you can get from defrosts. Since the armor defrost is new it will take time to see what values should be set for it. If its too little then there isnt much point to it. But neither should it be too high. Unless I am mistaken armor is now 10 points per defrost. So if someone defrosts 5 teammates, for 50, he should get some benefit for his team play. Considering a typical round is 35-40 points of damage not including location modifiers, or 70 for sniper rifles, 50 points of armor isnt that much. Also considering the armor doesnt regenerate.
But as said before it makes stopping power a much more useful perk to have. Also means you are not going to kill another player by shooting him once in the arm or the foot. Which is the stupidest part about hardcore. IMHO hardcore is only there for games with players that dont want to bother with getting torso or head shots. As for hit locations, for those that dont know, in the game engine if you shoot an enemy at his side a shot at the torso area will often hit the arm. Which is logical. Something to keep in mind when shooting enemies moving at right or left angles relative to your position.