It depends upon a lot of things. I found a walker I liked at a second-hand store for $10, got it properly adjusted for height, and took it to the hospital with me both times. I used it while in the hospital and for a week or so after I got home. I used it at night for an additional three or four weeks just to be sure I didn't fall while I was half-asleep and going to the bathroom. I used crutches for about a week, then I became comfortable with one crutch (if using one crutch, make sure you use it on the opposite side from your TKR to promote a healthy gait). Eventually, I felt comfortable with a cane. Then I used no walking aids in the house but still used a crutch or a cane when I was going outside.
It all depended upon what my knees were telling me they needed for support. On my first TKR, I used a cane long after my OS thought I didn't need one because my non-operative knee was giving me trouble. After my second TRK, I took crutches or cane on my first few extended walks just to be sure I maintained a good gait. If I felt myself getting tired or weaker, I used the aid. If I didn't, I carried them.