2hour extension is normally 1100-1300 or 1200-1400. No right to expect 4pm

Even if hotel is willing you shot your self by agressively demanding 4pm. Not unusual for hotels to chrge xx/hour for early/late checkiin/checkout especially if exceeds a 2hr extension, though limited to 6pm after which whole night needs charging
So no, demanding 4pm the hotel clerk is correct to charge you their xx per hour surcharge. Maybe that was 4x10eur/hour 1200-1400 , but may have been 2x 20eur/hr 1400-1600 with 1200-1400 foc

Also depends on occupancy percentage rates for night of day you leave etc eg
o if hotel will be almost full that night of your checkout hotel may say no because of that
o too many guests request late checkout, not every checking out can be given a late checkout
o if as spire you had a room cat upgrade, (or booked a higher cat room) remember less rooms of that type will exist so again hoyel needs say no
o if only ask at last minute say checkout time on morning of departure when hotel has already planned for the day. it is polite to ask at checkin not night before or day itself
o smaller hotel, less number of rooms,
o logistics, ie 1100 checkout hotel only employs room-maid-cleaners during morning say 7am - 2pm , not the 5pm needed to makeup late c/o rooms as needed if you keep room until 4pm instead of 1pm extension