Is your 6 minutes of black screen at the beginning of your exported MP4?
According to the Source and Project times shown, there is a 5:19 difference. You might have deleted clip and there is a 5:19 space at the beginning timeline. I can’t see the whole timeline in either photo. To scrunch the timeline, hover the mouse over the timeline zoom tool, and just scroll up or down to resize. It appears to be a real easy fix, I just don’t have enough information to help you any further.
If it’s not a deleted clip, try exporting the clip again.