Do not ever rely on anyone who, as part of their job description, installs Microsoft Windows, under any of its many monikers, to be on time. The only way it is possible for one of these lowly workers, is to master the art of estimating the CPU speed, RAM, available disk space, disk defragmentation, etc. of the machine to which Windows is being installed on. This is not an easy task, as most of the time these details can not be known until minutes before installation.
If the computer is extremely lacking in the above mentioned hardware items, the installer will be forced to sit and stare at the progress meter in agony, thinking of all the wonderful things she could be doing instead. More importantly, the installer will be late for, or even have to miss any appointments, meetings, etc. that were scheduled near the time of the installation. It is not practical to assume that the installation will take as long as on the worst possible hardware, as this would not allow the installer time to do anything at all.
So i guess if you're getting pissed off at someone for being late, or not showing up, just remember, they might be cursed with the foul job of installing Windows, and it's not necessarily their fault.