If you fly frequently there are chances you have seen some delays in departure where you end up waiting in the aircraft sometimes for multiple hours.
Almost every time that happened I remember the PIC announcing something in the lines of We will try to make up for the lost time...
And they manage to do a very good job at that. One of my recent flights was delayed 2 hours on departure but arrived only 1 hour late.
Its quite exciting when they say that, its like wow he/she will speed up! but how much leverage do they have to accomplish that? I'm sure there are commercial as well as regulatory requirements to remain within a range but how broad that range is for general commercial aircraft?
The aerodynamics and engineering part of this problem I know about, I'm mostly interested in the commercial aspect of it. Are the speed ranges set by commercial interests?