As of today, there are 3 major skips in the game that each save a minute or more and are pretty much needed to get a good time:

1.Maze skip 1: Just walk beneath the drill and activate your rocket, this will take you out of bounds. The angle to fly through the darkness and end up on the right part is the importent part here, but easy to learn. saves about 1 minute

2.Maze skip 2: At the start, walk backwards into that hole and activate rocket. Now you can use a combination of pressing up (keep pressing it) and grinding along the wall to get out of bounds, then fly right to the end.
saves about 2 minutes

2. Power Plant skip: saves a lot of time over the regular strat, and about 15 seconds over the other skip. Maybe the hardest one, this one saves you the long walk up the facility by using the flying glitch. This is how to do it: Right after you leave the small room in the begging, you turn left and face the wall, while standing at the very top of the ramp. You then equip the grappler and aim at the wall. There is a spot you can shoot at, and you want to hit the very left of it. This may require some practice to get spot just right, but once you got it, you will swing to the wall. At this point you turn left till you face the wall and press forward (up) on the keyboard to swing into it. If you done it right, you should now be kinda stuck in the wall, not seeing jimmy complete, just a fraction of him. this is where you release the grappler (pressing space will do) and fall to the ground. IMPORTENT: you need to land here. if you dont, the flying glitch wont work and you have to reset. Once you landed, just jump of the edge and wait till the jet-pack activates. Use the bubble, then either cancel it. The jetpack will disappear, but the flame is still there. Now just turn around again, jimmy will now start to move up. Avoid the Pipe of the left and press forward to fly towards the end. About the time the ceiling of the power plants starts to disappear you want to press jump to cancel the flying glitch and land on the pipe on the very top. Now just use the bubble to move along it till the end and jump of the edge, then press the back key to move into the warpzone and finish the level. saves a lot of time over the regular strat, and about 15 seconds over the other skip.