The ending twist was revealed shortly into the episode (if you know your sci fi). When Zane gets zapped by the robot flying machines the 2 realities blur very slightly. This took away the impact. You should also be able to work it out on the fact that Carter and Jo would NEVER get together. They are best buddies nothing romantic there.
I would guess no time has gone passed. The 4 year thing is just in the computer sumulation