When my first element failed, I thought I had to buy a replacement of the same brand AOSmith. Only one vender around here but right on the way to work Plumbing supply store. He told me how to do it. I probably paid more than at a hardware store, but well worth it for the added info.
The water stays pretty hot for a 2 -4 days if you don't use any. Of course the more you use, the cooler it gets.
Oh, yeah. I think I left out turnng the faucet off again. If left on, air would go in and water woudl come out of the WH. Turn it off.
This is especially valuable for plumbers, who don't want to spend an hour draining the tank and an hour filling it before they can turn it back on, either for free or trying to bill the customer for 2 more hours or more.
But it went very smoothly for me. Maybe 3 seconds with nothing in the hole, and another 5 seconds before I started screwing in the new element. Less than 3 tablespoons I think.