Can I cook meat on low for half the preset time? I have a Crockpot that has preset settings to cook on high for 4 or 6 hours or cook on low for 8 or 10 hours. The Crockpot model is "Crock-Pot® SCCPVL605-B Cook and Carry Smart Pot Slow Cooker" and the control panel looks like this:



However, I've noticed many recipes call for cooking for shorter durations on low such as this recipe that calls for cooking for 2-3 hours on high or 4-5 hours on low. 

First of all, this seems odd as the official crockpot website conversion table says the equivalent of 3 hours on high is 7 hours on low (not 4-5). I'm partial to the low setting as I feel it will probably taste better. So should I just set it to 8 hours on low since it's close enough to the conversion chart's recommended 7? 

Or should I follow the recipe as close as possible and use the 8 hour low preset and remove the food after 4 hours? A potential problem with this approach is that I've read that with the presets a certain amount of time is needed to reach the "simmer point" and if you remove it too early your food may not reach the desired internal temperature and therefore be unsafe to eat.

Ultimately, my question boils down to which preset should I use and for how long when the presets don't match the recipe?

Also, please note that my question is different than this question on overcooking as I'm wondering if I may be undercooking.
I would put it in on the right temperature and take it out after the time stated in the recipe. If you're worried about whether the food is done or safe to eat, use an instant-read thermometer to take the temperature. You can check the FDA's website for safe cooking temperatures:
https://www.foodsafety.gov/keep/charts/mintemp.html

As to your concern that the simmer point is different with different settings. If it were different enough to affect the situation you're describing above, your crockpot would not be safe to use. There's a minimum time that your food has to get to a safe cooking temperature no matter how long you are cooking your food (I don't know the exact time, but I would guess around 30 mins). Many slow cookers initially cook food at a higher temperature to get it to a safe cooking temp (above 140 degrees Fahrenheit) and then lower the temp to the designated cooking temp.