I remember answering a question about whether or not I'd be willing to take a dog for longer than a week when I signed up, but now I can't find it.
I remember the question you’re asking about as well, but when I went through all of the pages in settings I couldn’t find anything either. Maybe try contacting support about it?
In your Profile, Details, Additional Information, the last question is whether you will accept stays longer than a week.
Like Jennifer commented, from www.rover.com/account/profile/rates/ look for Extended Stay, enter number of days along with a much higher rate to be applies when someone wants to book a stay over that length of time. If your regular rate is $30, and you don't want stays longer than 7 days, maybe you'd enter 8 for days and $100.
I don't remember the question you mentioned, but under Services & Rates - Rates, you can change your extended stay limits which includes # of days and price.