The regulatory authority in the case of excessive discretion reports or the company accountants as schedules fall apart.
Back to your original Q - yes they could, but it would be impractical unless you were a small a/c with little or no refuelling, minimal ground services like pax boarding/deplaning/cleaning/baggage handling and a very slick performance/tech log system.
You are certainly being 'mysterious' here with quotes like
"in the example quoted 15 minutes is not realistic
but it appears the operator has used a time to fit the flight into the FDP." of which there is
no sign in your original post. Without more detailed information, I feel you will get nowhere with this thread.
