In the first pass I made a lot of small fixes to cover typos, drop down menus of the interface, sometimes the mouse, a transparent frame to have nice borders, ... but I didn't modify the timeline.
In the second pass I cut dead time, error that were erased, and other similar stuff that modify the timeline.
The first pass takes like x4 the length of the video, but the second pass only take x1/2 of the length of the video. (I had to fix a few details in the first pass, so I rendered it like 3 times.)