The usage of "Job Open for " field on Jobs & Experts plugin

Hi, I have a question about Jobs & Experts plugin. What is the usage of "Job Open for " field on Add new job section? I've tried to input Completion Date by May 14, 2015 and Job Open for by 7 days. I have no idea about the usage of "Job Open for" field. Can you help me to explain this or give me some example?
Thank you