It doesn’t matter if your project is agile or not. Someone wants to know the answer to this question before you’ve started. And, the larger the project or program, the more they want to know. It’s reasonable for people to want to know. And, it can be very difficult or impossible to provide an answer to this question. An iteration zero, no matter how long it is, will not provide you an answer. You can lead the organization by using the transparency that agile provides, and learning how to iterate and how to better the answer as you proceed.