aaaah, seeing 3 choices in postits, I hope this means on of the 3 will be developped before the release, then I vote here !
Plus, seasons could be 1 month of real life time, obligin people to farm all month along to help their community for a month of winter
When thinking about the length of each season you should not forget that the agricultural cycle is highly dependent to this. I am no expert but i think that most crops can only be harvested once per year. If this is not altered ingame i would not make a year too long (one week per season is the shortest i can imagine but four months for each harvest seems too long for a game.)
Also you must not forget those poor players who have their first spawn during winter or late harvest without supplies, shelter or social contacts on the server. Should they wait a whole month until they can start to play with a chance to survive for a longer period?
Or maybe the roughness of the seasons depends to the geographic position so that winter in the starting area would be less frightening.