The fermentation time of yogurt depends on your fermentation temperature and sealing degree. In summer, the temperature is generally above 20 degrees, and it takes about 10 hour for fermentation under full sealing. In winter, the temperature is generally around 10℃, and it takes about 18 hours to ferment under completely sealed conditions. It also depends on personal taste. If you like it a little sour, you can ferment it for a while. The longest fermentation time should not exceed 14 hour in summer and 26 hours in winter.