As far as I've gathered, there's the camp of people who wear bras as underwear all day, and people who only wear them for short times when they go outside. So changing them once a week would be very different depending on which group you're in.

I'm in the second one, and only wear a bra like one day a week when I'm physically at work instead of my usual wfh. And as long as the bra still passes the sniff test, it'll get worn again. That can be like 4-6 weeks in winter haha