Hacks are not a way to get more free time, they're a way to get more time to hack!
Unfortunately google isn't helping me find an old FoRK post that goes into greater detail and gives references.
I believe 'hack' originated from the hack-box used for young hawks (here hack refers to the hacked meat that keeps them coming back to the box); while 'at hack' young hawks would get useful hunting experience in a relatively unstructured environment.
Later hacking became used for both hounds and horses, again with the sense that going out on a hack is enjoyable and can certainly be useful but is contrasted with directed work.
How it might have made the leap from hawks, hounds, and horses to humans (of a demographic largely distinct from hunters) is still a mystery to me.
-Dave
