There won't be as many days in a year as in real life, so a battle would have to last something like two and a half hours for a day to pass in-game.

Edit: Deffcon beat me to it.

there hasn't been much in regards combat yet, and that has been intentional by the dev, however in the last Q&A Caspian said that 2 or 3 well placed hits will incap someone. So damage is going to be realistic. If you hit someone in the head with a club, they'll go down unless they have a helm on. If you have an armour piercing crossbow/bolt, 1 shot will probably do it, so a 1v1 fight won't be 10mins unless there is a lot of running away, infact a 10min fight will be somewhat epic or both people are heavily armoured with feathers.

Also if a 10 min fight lasted 2 ingame days, how would you notice in the grand scheme of things. If a light/dark cycle was uber realistic, then sure, but it won't be because you'll have a forever flashing screen and shadows will always change causing fps to drop, etc etc. But your character will still age 2 ingame days right? take 2 photos of yourself 2 days apart, can you notice yourself aging?

All being said though, your obviously going to have to suspend belief and let yourself be absorbed but the game, just as you would any other game.