I assume you talk about terminal 5. I'm not a fan departing from 5B or 5C but in most cases that's announced at least 20 min before boarding and you can easily

I assume you talk about terminal 5. I'm not a fan departing from 5B or 5C but in most cases that's announced at least 20 min before boarding and you can easily make it there in 5-10 min (most of which is spent waiting for the train). I experienced twice that the announcement came a bit later but then they kept the gate open later to ensure everyone makes it.