I think for standing tasks and not just walking, the ergonomics make such a big difference. DH is tall and while his legs don't tire easily, if he's hunched over the kitchen counter chopping, his back and neck get tired. I'm too short for our counters so if I'm going to be doing a task in one place for awhile I stand on a little stool. Chopping lots of veggies, for example, gets tiring for my shoulder because I have to hunch it to get the knife high enough to cut the veggies. I just put up with it for small tasks, but I will elevate myself if I intend to work in the same place for awhile.
Also, gel mats. They are your friend if you want to stand longer, as are clogs.
So when you're setting goals, consider the ergonomics. You may find you can do more than you thought with the proper posture and support. :grouphug: