It’s ready when you decide.
Most banana bread recipes indicate an approximate baking time. For example, this Bon Appetite recipe calls for 60-65 minutes in the oven.
Notice the instructions also say: “Bake bread until a tester inserted into the center comes out clean…”.
There is no set time and there is no 100% way of knowing beforehand when the bread is ready to be pulled out of the oven. You must test it and then decide if it’s done. It’s your call.
The same is true for any product, service, project, or talent you’re developing. You can set a timeline, and you can test all you want, but there’s just no definite time, and there’s no 100% way of knowing beforehand when it’s time to launch.
You must test and then make the call.