I had a meeting with a stakeholder who stated “I bet you wish I wasn’t in these meetings”. She said this because she kept changing what we thought the end product should look like. My reply was that it would be much worse if she came in at the end of the project and told us we had just built the wrong solution.
You have to take the time to get the requirements right. Be honest with all involved parties as to the amount of time it is taking to refine the requirements. The only thing worse than wrong requirements is a surprise in budget overages. If you give open visibility to your progress then management has the ability to shift priorities if needed.
In order to capture the best requirements use different approaches to help your stakeholders to articulate their needs. Use mock ups and matrix spread sheets to allow them to visualize and confirm that everyone has the same understanding. The goals isn’t to record every last detail, but to have the major landmarks identified so there are fewer surprises along the way.
Help the team members to understand that you all have the same goal. You want to create the best possible solution for the given business problem. If you do this everyone involved will do there best to outline a picture of what is to be built and you will be able to design an appropriate solution to fill those needs more easily.