Ah, these well-meaning people who haven't had a knee replacement, but who tell us how to manage it! Try not to listen to them.
As you recover, you'll possibly hear stories similar to a friend's friend's great-aunt Martha, who walked out of the hospital on day 2, hiked ten miles by the end of the week and was spinning cartwheels within a month. There are lots of stories like that, but they're all urban myths.
I have a friend who could have been the subject of one of these myths. He had a TKR and went back to work the following week. That's the short version.
The long version is that, yes, he did go back to work the following week, but only for two hours a day. He had a desk job, he was in a wheelchair, his wife drove him to and from work, and he was completely wiped out for the rest of the day, spending all his time in bed, apart from bathroom visits.