Striking and Winding Ability...

I would be afraid to put a time on it, when I say cold I mean the dogs had to really work. I believe to compare dogs nose power you have to have them on the same track at the same time.
The reason I am hesitant to put an hour number on any track other than a game cam pic or where someone saw and ran the game off is this, several years ago I had a pair of dogs I put on a hog track that I knew was 10 hrs old they took it in pretty good fashion, once after that I put them on a 45 minute old track where I watched the hog run off and stood there and waited for my wife to bring me the dogs and they didn't even acknowledge it. That really made me aware of how much effect conditions can have both positive and negative.
Now the dogs I said winded that track way off the mountain and took it have been hunted with a few different sets of dogs and have been able to trail any track the others could and I'd guarantee you there are dogs they can't trail with, thats the best I can tell you. They are just dogs not phenoms although those two occurances were extraordinary and I believe ti was due to perfect conditions.
They do quite often strike a cold track up to 300 yds off the road "when conditions are right". And I'd bet that they sometimes somehow miss rigging a really good track.
But how old a track a dog can take is very subjective due to conditions. When they winded those cold tracks I have always said conditions had to have been perfect or not only could they not have rigged it but could not have moved it had they found it on the ground. Once in a great while they rig a track that sounds pretty strong that they cannot make go on the ground, I always "guess" the scent has risen high enough they are out of the scent cone when on the ground but it is only a guess. The way scent and conditions work fascinates me and I don't expect to ever be able understand it all due to lack of intelligence and education on the subject. I'm sure that the folks that rig constantly have saw all the above scenarios and the majority of them are probably bear hunters that do not bait. When they bait they have a picture with a time stamp and can see the variation in what the dog can take.
What really amazes me is the dry ground lion hunters out west hot, dry windy and sometimes strike a 2-3 day old track and occasionally even catch a lion from that old of a strike.