Time is the process in which Stardew Valley proceeds. Each day is 20 hours, from 6am to 2am the next day, and each hour is sixty minutes. Time passes in ten minute intervals. Each interval equates to about seven seconds in real-time. There are 7 days per week. An hour of the game consumes 43 seconds of real-time, a day consumes 14 minutes 20 seconds from 6am to 2am, a week consumes about 99 minutes 40 seconds (about 1 hour 39 minutes 40 seconds), a season consumes 326 minutes 20 seconds (a little over 6 hours and half), and one year consumes 1605 minutes 20 seconds (a little over 26 hours).
At in-game 12 am, your player will become tired. If you are still out of your home at 2 am, you will stop whatever you are doing and fall asleep. You wake up the next morning in your bed, with a note in your mailbox that either a Joja Co team carried you home, Linus found you unconscious, or you were taken to Dr. Harvey after being found by a neighbor (if you're not married to him). You lose up to and including 1000 gold in medical fees or from someone going through your pockets, depending on how you're found.
Sleeping affects the rate at which time progresses. When asleep an hour becomes 100 minutes which affects processing times. Going to bed early means things will process a little faster in kegs, casks, and preserves jars, but may mean missing out on in game events such as heart events or holidays like the Dance of the Moonlight Jellies.
The world becomes dark at nighttime. If a light source disappears at nighttime, nearby NPCs will run away. The inside of houses will need to be lit as well as any spaces outside on the farm that you may still be working on once the sun goes down.
There are four seasons each year consisting of 28 days each: Spring, summer, fall, and winter. Each season starts on a Monday and ends on Sunday, with 4 weeks total making a year 112 days total. On the first day of each season, any crops left planted the previous season shrivel up and need to be cleared away with a scythe before any more can be planted (with the exception of cross season plants like coffee beans which grow spring and summer, corn which grows summer and fall, wheat which grows summer and fall, ancient fruit which takes a season to grow and continues to produce until winter, and tea leaves which can be harvested the last week of each season until the start of winter). No crops can be planted in winter with the exception of Winter Seeds and Powdermelon Seeds produce winter foragable plants (winter root, snow yam, crystal fruit, crocus, and holly) & powdermelon fruit respectively.
