I think I recall hearing that those instanced open field battles will have an approximate 24h time frame beforehand to set up troops fighting on both sides.
That leads me to wonder if you might be able to make a living out of fighting different factions' wars for money or just for the fun of it...
In Mount&Blade there is this multiplayer mod "Strategus" in which battles are scheduled very much like it sounds for LiF:
you can sign up for a battle on a web site and join the server when the battle commences. I haven't done it but this seems to be the system.
So do you think you could fight in scheduled battles all the time if you wanted and bring in your expertise and fighting power?
It seems to be the perfect playstyle for people who are easily bored by building houses or digging holes into the ground.
P