Good consultant actually suppose to ask those question to figure out what you need.
First define in plain English for yourself what you need and, if this is existing application, what is our major problem(s).
For better use of consultant time, if possible, try to split his visits. For example if you have DB performance/blocking problems you may need to get his advise on how to collect sample queries form trace, - this may take 1 hour, 1 day or 1 week or more depending on your application design and usage. Then you will implement their suggestions and again it may take time to see is if works or not.
if your intention is complete DB redesign - you need to prepare detailed description of your application, use cases, define what is UI for your database, and list major problems with existing design
If your concerns is capacity/scalability - you need to define where you expect your growth and how DB structude will support it
