How do you know when your startup is ready? (I will not promote)

First time startup founder here. I always hear the sentiment of "perfecting before launch" but does that mean you should rush to release a product before it's ready? How can you tell the difference between trying to perfect a product and having a product that is ready for market. Not sure if that makes sense. Is there a certain time limit? I see people who say they have been working on their startup for 1.5 years and others who released after just a few months. How do you know when it's ready? Is there some specific time? How do you decide what features are necessary or unnecessary?