It is a constant preset temperature with the cooking times set by yourself. For example, when I cook a normal sized chicken, I set the time for 2 hours, assuring that the chicken will be well done. Average times for various food products are provided by the manufacturer giving you the option to set your own cooking times according to your individual preferences.
No you cannot control the temperature on the unit, it is pre-set. So it all depends on what the item is and the weight of it, this determines the required time-length for cooking. if you go to the Ronco website and look under "manuals" or "Recipes" It will give you a lot of info on cooking times for different items. I LOVE my Ronco and use it almost daily !
It's a constant preset, BUT there are two postions for the spit rods (great name, huh?). The closer you position the spit rods to the heat elements in the back the faster your item will cook. Likewise, if you're not careful, positioning in the rear position can dry out your food. Personally I'd recommend using the forward position and waiting longer for the cooking process to take place. It will be moist and you have more control over doneness. Be sure to use a meat thermometer so you know it's cooked enough.