I would say that 99.9% of ATCOs take slot times very seriously especially as MATS 1 now states that the slot time is an integral part of the clearance and should in thoery be passed with the clearance.
All it takes is for a sector overload to trigger an investigation and with the airfiled movement log any transgressions will soon come to light.
A Manager ATS certainly has no authority to break slots and if tried on me would be politely told to sign the watch log and take over the watch - swiftly followed by submission of a 1261!!
