But i'm wondering about the actual time before those kind of preserved food can last before turning inedible.
Heresy ! spoiled =!= inedible
Spoiled food is good for you !
While non spoiled food is better, and should be prefered, spoiled food can save your life. Spoiled food, even from 10 years ago, won't kill you. It will, at worse, give you a ~-10% sickness, and you'll vomit a few times. It's actually a very good way to get your nutrition up, since vomiting will empty your hunger bar (hunger bar is your enemy in your quest of survival), and you'll be able to eat again (spoiled food).
/!\ Spoiled food must be cooked to be edible, spoiled raw food is worthless, while spoiled roasted food is useful. If you don't have any way of long preservation, roast the whole, eventually keep in a cellar, and eat spoiled food.
Snuck up on a sleeping reindeer. I thought it would provide enough food for quite some time, so I stabbed it in the neck. Twice. It got up and... ran away. Eventually the blood trail stopped. Apparently, its gaping knife wound got better.
Then I began the tutorial quests to get some free loot. I found a squirrel in a tree for the "kill something and carve it up" quest. Cut down the tree, squirrel runs to the next tree before I can get a hit in. Cut that tree down and a wild canine creature comes along, murders it, and runs away before I can even look at it. I still got credit for the kill, though.
First tip : aim leg for reinder to not run away. Though if you don't have a very good weapon (knives aren't really good, the hunting one can be good because of bleeding, but that's all), it can happens that the animal will run away.
Tip on squirrel : squirrels live in trees and will not leave a tree except if it's cut down. Which means : don't cut the tree a squirrel is in, it'll run away very fast to a next bunch of trees. Other than that, they can move from trees to trees.
An easy way to kill them is getting them in a group of tree, and since they won't move away from that grove, throw things at them (rock especially, not stone). They won't try to escape if it involves getting down of a tree.
So, the way to kill them is to trap them in some trees.