Did every knight train in such a fashion, certainly not. When they refer to seasoned warriors, that had to do a lot with physical fitness. Those who survived to fight more are the group that I referred to.
First, you're using the word knight in a sloppy fashion. Putting on armor did not make you a knight.
If you were a knight, you trained, and you trained as part of the order you belonged to. If your liege felt you were not training in peacetime, there were a number of punishments ranging from social humiliation, to forced training to judgment served against you involving loss of real property and pay. The entire point of tournaments during peacetime was to encourage knights to remain in training.
What most people think of as armor is plate, and more often than not, it's ceremonial parade or jousting armor, vs armor worn for fighting.
There are lots and lots of contemporary images and manuals regarding knightly training, armor care, and histories which refer to actual events.
They still did not wear armor all day every day, even during war.
Armor was designed to be worn over at least two other layers, and knights removed all or some in order to sleep. Sitting around a campfire in full armor would be foolish; it's going to get awfully hot. Remember under the external metal and chain (and often a furred cape) there are likely thick leather pads, and thick wool and linen and or silk, and padded undergarments to assist in preventing chafing and for additional protection from blunt force. It's
hot. Froissart writes about people becoming dehydrated while waiting for orders in camp.
Moreover, armor frequently needed care; those leather straps and flange pieces might have to be replaced every day during an active period, so often, at night, the knight's squire and staff would be repairing the wear of the day.
You'd remove armor or parts of it when you're not actively expecting to fight, and you'd change your armor based on the kind of fighting (on foot, on horse, etc.). If you're traveling, you might remove parts or even just wear a habergeon and chain, along with a helmet, again, possibly just leather. You'd reduce the amount you wore in order to sleep too, since guards would be posted.
When I studied it was probably before you were born so I don't remember what books they were and it was well before there was even the concept of an internet.
I was born in the 1960s. I've been a card-carrying Medievalist since 1985, with my first graduate degree. I earned two more after that, culminating in a Ph.D.
I've worn armor made for a mercenary in the 1480s, and gotten on and off a horse in it, by myself, and participated in display combat using a blunted sword weighing just over two pounds.
I worked
here as a docent and researcher in the summer of 1984 before it became part of the collection
here.