Vitek: Hello,
is there some time limit either for campaign as whole or for the continents.
I can't find any but now I am in mission and in the middle of it I get animation with text "Unopposed Shadowlord crushes Aer with an iron fIst.", or something like that and the game ends.

It is not the time limit of the battle. It has something like 20 turns and this was around turn 5 when it happened and it was when enemy had only few units left.
So it was early in the mission. But I took time with the last one beacuise I refused the surrender offer and then ended up hunting two stray flyers all across the map until last turn, so it is possible I hit some limit for the world?
It happened to me twice in the same map already.

It is on the second world and I already have option to attack the castle but I wanted to fight other battles first to gain money and XP.

Vitek: Thanks for the reply, even if it is this late. :-)

But it is not what I was asking about.
When I get the 'time is out' message it was early into the next map, far from time limit of that map.
I only mentioned the surrender thing to say I wasted a lot of turns previously and asked if it has any effect on overall time limit. More precisely if there is any campaign or world time limit.

Man, it's long ago. It made me stop playing this game and I haven't returned to it since then.
I need to try it again sometime.

ConjurerDragon: That is not a time limit. If you refused the surrender of the enemies then you have to destroy ALL units of the enemy on that map. If you don’t you lose that battle and the game.

So either accept the enemies surrender when it is offered - or be faster to hunt down every single of the enemies units if you deny the offer.