Thanks to Canida, he gave a great addition below in the Comments: "A necessary addendum to Step 1: verify this breaker actually maps to your hot water heater. Our breaker box had a full set of labels that turned out to be randomly applied!"
Feel free to check out my blog here!
Step 1: Disconnections
1. Locate your Power Box on your house and turn off the breaker labeled 'Hot Water Heater', ours was H/W Heater.
2. Remove the plate on the hot water heater then remove the wire nuts.
3. If you have conduit running to the wall then remove the plate and the conduit.
Step 2: Installing the Conduit and Timer
1. Start by locating a stud and then screw a srew in until it is about 1/8" shy of being flush with the wall. (Notice I did not attach the box to the wall permanently, that is why it is at an angle, I attach it later once everything is measured out and dry fitted together)
2. Install the conduit to the original cover plate on the wall. I decided to attach the conduit to the side of the box because the wall mount was directly above the box, it is up to you based on the location of the box.
3. Install the conduit to the box and run the wire through and then trim the wire with about 3-4" excess to be able to attach to the terminals.
Step 3: Wiring the Timer
(Follow the instructions in case they have changed)
1. Pull wires through conduit and strip wires back a 1/2".
2. The wires from the hot water heater will be set to the right terminals, wires from the house go on the left. From left to right, Terminal #1 black from house, #2 black from W/H, #3 white from house, #4 white from W/H.
Step 4: Finish Wiring and Close Up
1. Secure wire nuts as they were before when you started.
2. Attach the ground wire to the ground screw.
3. Attach the Cover plate on the W/H.
Step 5: Setting the Timer
1. Put on the clear plastic cover over the wiring.
2. To set the time you pull out on the yellow dial and turn it to the correct time of the day. DO NOT adjust the arm that points down 90 degrees.
3. Screw on the 'ON' and 'OFF' adjusters at the correct time and you are finished.