How much leverage do commerial pilots have on cruise speed? 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?
There is something called the "Cost Index" - it is basically how you choose between speed and fuel economy. Company dispatchers, after knowing that a flight has been delayed, will calculate this value, and the pilots simply input the updated value into the FMC (Flight Management Computer). That will instruct the autopilot to output more thrust, i.e. fly faster, but less fuel efficient.