This is a generic and probably not very well posed question, although triggered by a specific recipe.
The original recipe says to sear a pork loin in a pan, then deglaze with white wine and finally put the piece in the slow cooker for 7h on low. Their ingredients list says 1kg of loin.
On the other hand, as I want to cook only a 500g piece and I know that the "low" of their device and the size of the device itself may be different then mine, I decided to use the only reliable instrument when it comes to meat: the thermometer.
I set an alarm at 70°C, that according to some search sounds reasonable for pork loin.
Such temperature was reached after not even 3 hours on my "low" setting!
Now, it can totally be that the recipe authors didn't aim for the same temperature or that they just wrote a nonsense figure.
Also, since that smaller pieces cook faster is true for every device, let it be oven, pots, pans etc. What is bugging me a little is: not even half the time?