My preop baseline for several years was 1 - 1.5 miles nonstop outdoors.
(I was braver about getting out on my second knee replacement; with my first I was terrified of simply misstepping (as one does preop with an unstable meniscus) and literally shattering my implant.)
With my second knee I believe my first outdoor walking, with walking stick and husband, was at 4 weeks, and brief.
I recorded that on post op day 33, I took my first solo walk. With my walking stick I went down our rather steep but not long paved driveway, across the street to where there's a sidewalk, and walked slowly past three houses (guessing each lot about 60 - 70 feet), then turned and went back.
At six weeks, I was walking just under 1/2 mile, with a walking stick. I stayed at 1/2 mile for quite a long while as a necessary plateau.... because twice I advanced too quickly and spent a few days in the ODIC (OverDid It Club) ...
At eight weeks, I graduated to walking my 1/2 mile without the walking stick!
At 12 weeks I was walking a bit over 3/4 mile.
At just over a full three months "I am comfortably taking a one mile walk most days, often with a second half mile walk (walks are early morning and after dinner to avoid ongoing afternoon warmth). A few days ago for the first time I did a mild-moderate (paved road) hill loop behind the house, about 3/4 mile, and was pleased to take it at a good pace and zero ill effects same or next day."
Week 15 - 1.8 miles non stop.
Week 16 - 2.25 miles non stop.
Five months - a visit to a friend who lives on a hill in San Francisco. Besides tons of stairs, I walked 3.5 miles - half of it on level, with a single five minute break before beginning the hill climb. Since then I have walked 3 miles nonstop several times.
My goal for this year was five miles and frankly the main limitation is the time it takes and where am I actually going? So I have been rethinking it, away from miles, and focusing on increasing the time spent on trails in our hilly regional park.