3hr interview next week

I am stressing out because I have a 3 hr interview next week for a big company. I will be interviewing with 6 different people all for 30 minutes each, which is why its so long. All of the people are directors and vice presidents of the company (Research and development director, vice president of quality assurance, etc) and I don't know how to prepare. This job required 0-3 years of experience and is more of a supporting role so I never thought it would be this extreme. Any interview tips would be greatly appreciated.