5 - 30 minutes
My wife's iPhone wasn't lasting the day with moderate usage, so it was time to replace it.
The repair went well. Two things were a bit of an issue. First, your guide needs to call out the proper way to bend the battery connection cable to get it to fit back into the iPhone. Second, I used the plastic opening tool to gently pry out the battery as indicated. It however broke the tip of the tool off and I had to use the other one. They need to be a little more robust, or need a recommendation to use something else.
Use the larger plastic opening tool to pry the battery out and bend the battery connector cable to match the existing iPhone battery exactly.