i concluded it in this way
,i have two senarios
1.wake up,car is started after few hours,brakes are cold,i brake hard ,the car stops
2. i take several drives since i woke up,brakes temp is normal,i brake hard,car takes longer to stop
my braking is usually hard at times,say about as u mention i apply hard brakes at 100kph,that time interval can cary from 30secs-3minutes