Is every season taking a whole year?

i'm going to say yes, that one season is one year. but i could be wrong :)

Generally a TV season can vary from 15 o 16 episodes up to 26 o 27. So the season will last about 6 months at a time. Used to be almost all shows were at least 26 episodes with the advent of Cable networks that has changed.
I don't care much for the gorra, cap Booth is wearing it's just not his style some how.

Yeah I would say that every season is one year..

They had navidad in season 1 in "The man in the fall out shelter"

I can't remember about season 2.. that's the season I've seen the least (I'm going to buy it)

In season 3 there's also navidad in "The Santa in the slush"

In season 4 tu don't have a chritmas episode but a winter episode
(wich is kind of the same, and it still indecades that a año has past) in "Fire on the ice"

I hope it helped ;)