Like Bajantara said, it all depends on how fast you pick the crops - is why the longer you been playing seems to take longer and longer for crops to come up because you have more farmers than you did at the beginning of your Village. If you are putting everyone in the village to gather crops when they come up, it wont make the next crop come up any faster. Just like in real life - Crops are "seasonal" and have a specified "time" or "cycle" when they will be ready for harvest.