A year consists of 4 seasons each with 3 days for a total of 12 days a year by default, this can be changed in settings though and can go as high as 28 days a season.
Seasons can be disabled in different ways, "seasonal growth" can be turned off so you can plant and harvest crops regardless of what season it is. You can also disable snow separately, there is also be a "fixed visual month" setting which means you can "freeze" the visuals of the game to look like a certain month of your choosing ie. be constantly October for example, this however will not effect how crops are harvested or how they grow they will act like there is no seasons instead.
If the season length is changed mid season the new season length will come into effect at the start of the new season. To compensate for the longer seasons you can now sleep at any time.
The crop calendar shows when different crops can be planted and harvested. Crops now have a demand so you will have to keep an eye on when is the best time to sell certain crops based on the season, you will have to store them until the demand is high enough to sell.
There are 4 seasons, each with different mechanics and visuals
Spring is defined as March, April, May. In spring time most crops are planted with the exception of some crops such as but not limited to wheat, barley and canola, theses are planted in fall. Crops are typically not harvestable during spring. In spring, trees start to grow their leaves in vibrant colours.
Summer is defined as June, July, August. During summer time some crops are harvested such as crops planted during Fall like wheat, barley, canola etc. there are also other crops such as potatoes and sorghum that can be harvested as well. In summer, trees mature into lush green trees. Summer is a great time for grassland farming such as making hay or silage for your animals.
Fall is defined as September, October, November. In fall some crops can be planted and the rest of them can be harvested. During fall trees turn brown and yellow.
Winter is defined as December, January, February. No crops can be harvested during winter, but cotton can be planted in the last month of it. In winter the ground becomes frozen and covered in a layer of snow, trees loose all their leaves and it can get icy. Snow ploughing can be done in winter to keep the roads clear.
You will also need to plan ahead when it comes to feeding you animals for the winter, you will need to store enough food for them as nothing grows or can be harvested during winter. Winter is also a great time to deal with your production chains if you have no animals or time to spare.