Garages work on book times.
Sometimes it goes to plan , sometimes it doesn't.
This is why a garage for example will quote 2 hours to do front discs/pads.
The book time will be worked out as an average, so sometimes they might be done quickly, sometimes it might take a bit longer.
Its ok if everything comes off easily, but would anyone be happy about paying more if it doesn't come off as easily? probably not.