In fact, it depends on the type of seeds you sow.
The time it takes for each type of seed to be ready for harvest is shown in the store next to each bag of seeds.
Note: A "day" on Town Farm is 20 hours. The pineapples that grow in 3 "days" are actually ready after 60 hours, or 2 ½ days. They therefore go to waste after two and a half days. You have 5 days instead of 6 for harvest From the moment you have sown!