Earlier quoted context omitted.
(I've worked in an FC for over a year. I'm an L1, not a PA or manager.) Most functions in FCs are "direct": they have rate expectations that are automatically tracked. Every minute you're in a direct function counts toward your rate. You can go to the bathroom whenever you need to, but it'll lower your rate. (Some functions are "indirect", meaning that they don't involve use of any digital tools and so can't be track…
So, in short: You might get written up for taking a bathroom break if the bathrooms are far away from where you work?
If you have to go down four stories to get to the bathroom, on the other hand, it'd be pretty hard to maintain the rate, and if you don't maintain the rate you'll probably get written up for that.