The operative word being "try."
They aren't necessarily looking for 29 minutes from each courier, but they are looking for improvement from the station as a whole. I've never seen a station hold each employee to whatever number was stated. I've never seen a station that made some half decent overall progress get hassled much. Don't be the station that doesn't make any notable progress or else a senior will come in with his one size fits all plan to make the progress for you and it won't be fun.