If you are doing the rear lowers, it should take you about 1/2 hour per side MAX! It's not hard at all. Use a deep socket, just a hair smaller in diameter of the sleeve, to push it out. It doesn't take much effort, just a socket and a hit or 2 with a hammer. Once the sleeve it out, the bushings will come right out. For installation, put the bushings in and tap the sleeve in with a hammer. Make sure you lube them well.
The rear uppers will take you more time because of it's location but its the same procedure. I say 2 hours for all bushings should do it.