This is true but beware. They've failed to turn up twice now to install my brothers broadband and we're not waiting 10 working days for a response from the CEO team as every other level of support cannot help.
The installation date for an appointed order is determined by the availability of Openreach engineering workforce in your location at the time.
As for attendance on the day, this also is a dependency on the engineer, or alternatively the quality of the data passed to Openreach during the sales process (i.e. correct address).