When you first latch onto the swingling, a billboard states: “Find the end of the line… but which end?” The fact that you got to the dead end means that you are at the wrong end of the line and that you have to go to the other end.
So how are you going to get to the other end, when the conveyor belts are moving the wrong way?
Well… Here’s my advice to you. Do you see the orange and blue striped square? If you swing your third mass directly past the square, then the countdown ticks down. When the countdown reaches zero, something special happens.