I'm sorry L1Technician but your information is incorrect.
The "reset" button on the back of routers is what is known, in full, as the "Factory Reset" or "Factory Default Reset" button. Holding this button for a prolonged period of time will reset the router back to its original clean state. When this happens the router will automatically reload the firmware settings which were set when rolled out of the factory, hence the name "Factory Reset or Factory Default". This is helpful when you can no longer gain access to the router's settings but have physical access, either because you can not log into the router due to a lost password or the software is corrupted.
The time it takes to factory reset a Home/SOHO router varies - suggestions from professionals and even network hardware manufacturers vary from 15 seconds to even a full minute. This is highly dependent on how the reset feature was designed for the router. One thing is for sure across the whole board - they do not want the feature to be accidentally tripped, which is why measures are taken to prevent such an occurence, from a long trigger time to a button which can only be pressed using a pin (or small ballpoint pen).
Please note that John and I are both experienced and certified network professionals. We have reset a lot of routers in our time.
Addendum: There are several types of resets. Factory resets are not synonymous with Hard resets, or Soft resets.