Smash the garlic, thyme, rosemary, orange zest, and lemon zest in a mortar and pestle to a coarse paste. Stir through the olives and season with salt and pepper. Set aside until needed.
Dry the skin of the pork loin then use a jacquard to pierce hundreds of small holes in the skin. If there is time, rub with salt and chill overnight with the skin exposed to the air to dry it out.
Layout the pork loin with belly skin side up. Wipe dry then rub the skin with the residual lemon skins from juicing and sprinkle generously with salt, rubbing in as much as possible.
Flip the pork loin so the meat side is up. Spread the herb and olive mixture evenly across the meat.
Roll the belly flap over the loin to form a log. Tie tightly with the butcher's twine, evenly spaced about 2-inches (5cm) apart to hold it together.
Slide the rolled pork on the spit rod through the center of the meat. Secure with the spit prongs. Using fine wire, bind the meat a second time for additional insurance in case the string breaks.
Roll the spit in your hands to see if it spins evenly, if not adjust the counterweight to make it smooth and even, which will help for an even cook and place less stress on the motor.
Cook the pork until a meat thermometer reads 167 degrees F (75 degrees C), about 3 hours, or to your preferred doneness.
Remove the pork from the spit rod and let rest for 15 to 20 minutes before slicing.