Is this the same question as, "How long is a string?" If you're walking for fitness I'd suggest an absolute minimum of 2 miles a day, walking quickly. I usually walk between 4 and 7 miles a day. It's a great time for thinking.
I think that the steps are not that important and that you should just try to take long walks and not pay attention to questions like "How much time has passed?" or "How much longer till I reach my goal of ____ steps?"