As an electrician at the job site I would consistently look for work around knee level to give me an excuse to kneel and get off my feet. For years I've put up with heel pain after about 4 hours on my feet, even with nice timberlands or equivalent work boot.
Now, these aren't magic. I don't last all day without the pain, but making it 6 or 7 hours is typical and by the time the pain gets unbearable its time to call it for the day.