To do the skip you first have to get to the part to where the room with the 2 cubes are so after you run for around 15 or so seconds. Once you have the room unlocked go to the door then slowly move back until your on the slope then come the way you came. Once you go through the door the easy part is done. Now you have to use your jet-pack and get to the floating beam then fly up then land on the invisible floor. Run to the other side of the room where you unloaded the beginning section (you won't fall in) walk backwards until you fall. Once you start falling immediately move forward and use your jet-pack. If you did it right you should now be in the side that has 2 cubes stacked and a switch nearby. Grab a cube and this part is tricky line your self up with the button and jump and let go of the cube when it goes through the wall. If you successfully did it you should have the cube on the other pressure plate. Once that is done use the other cube on the pressure plate and now a cut-scene should start. After that use the switch that is by the pressure plate. It should open a portal. Go through it and start flying immediately. Turn towards the map and go to the beam (you must be flying during all of this). Once your on the beam start flying to the big door and land on it and land on the floor after all that disappears. Walk forward until a white door appears. Go through the white door and you're done with the chapter.