The operating temperatures of a refrigerator should be 0 to 10 degrees Fahrenheit (preferably 0 to 5 degrees) in the freezer and approximately 38 degrees in the crisper area of the main box. These should be considered the normal or desired operating temperatures. However, if you "max out" the thermostats or hot wire the refrigerator you should be able to get temperatures down in the low thirties (or even in the twenties depending on the conditions of the day and many other factors). The freezer temperature won't fluctuate very much, however. If a refrigerator is left unopened for days, the temperature of the freezer will actually rise slightly because the thermostat sensor only monitors the main box and calls for cooling only when it needs it.
Don't put too much emphasis on how cold your refrigerator can get. If you have a thermostat that cuts the cooling cycle off at 34 degrees and all you really desire is the normal 38 degrees, why give it another thought? The important thing is that your refrigerator maintain the desired temperature.
You will find numbers, arrows, hash marks, and probably other things used as markings on thermostat knobs, but you won't find any indication of what degree a certain point on the knob will give you. This is because the thermostats in RV refrigerators are not that precise--nor do they need to be. As long as a thermostat can keep your refrigerator at a reasonable temperature, it is doing it's job. If your neighbor's refrigerator maintains a temperature of 38 degrees on a setting of 2 and you have to turn your thermostat to 4 to get the same temperature, there really is no problem.
An empty refrigerator should show signs of cooling (a definite coolness to the touch) in the freezer within one to two hours after being started. The lower box should get down to temperature within 6 to 8 hours. Overnight is the best way to get a refrigerator ready. A refrigerator filled with warm food will take considerably longer to cool down, because the cooling unit has to remove heat from the food before it can reach the desired temperature.