By how much should I shorten the cooking time of a slow cooker recipe if I'm only using half the meat? I'm thinking of making either this recipe or this recipe for pork tenderloin in a slow cooker.
As easy as a slow cooker is, I'm no slow cooker expert, and have run into problems where the meat ends up seeming &quot;dry&quot; (even though it's literally soaking in a sea of liquid) when I mess up the amount-of-meat-to-cooking-time ratio, either by using a smaller cut of meat than the recipe calls for, or cooking for longer than the recipe calls for.
Both of the recipes linked here call for 2 lbs. pork tenderloin, and I have a 1 lb. cut.
The first recipe calls for 7 hours on low, and the second one calls for 6-8 hours on low.  So if I only have half the meat, by how much should I reduce the cooking time?  I'm guessing halving the cooking time is not really the right move.
You should probably not reduce the cooking time by a lot, if at all. These recipes assume you are keeping the meet submerged in liquid at some constant temperature for several hours. Assuming your tenderloin is not somehow less thick than a 2 pound cut would be, nothing in the recipe changes. The core temperature of the cut won't take any less time to get up to temperature, and the lower thermal load from having less product will also not affect slow cooking.
Ideally, have some flexibility in when you expect to be done cooking and stop when you have reached the desired results, rather than after some arbitrary period of time.
Apart from that: if you are having problems with meats coming out dry, you might want to check out this question and answers. To summarize: cooking lean meat for long times is usually not ideal.