I could comfortably walk about a half mile round trip by the second week; my main issue was just that I tired easily. (So I could go for longer walks, but then I'd need a nap.) By week 3, I had no significant pain except when sitting on hard surfaces for several hours.
Brassard had us up and walking by 18 hours post-op, and on day 3, the recommendation was to take a circuit of the residence (which was about a 10-minute walk, up and down two flights of stairs) every hour or so. I do think it helped to be active as soon as possible.