It means that on average, it takes customers only 7 seconds to go from the first page to another page. I'm stressing "another page" because the Average Time Spent on Site is calculated as the time difference between the timestamps of 2 values.
Note also that if users exit your site from that first page, then AA won't include that when calculating the time spent, because there is no next hit for it to calculate a time difference. So if your first page has a high exit/bounce rate, then the Average Time Spent on Site calculation will definitely be affected by that behaviour.