Clean the chicken by first removing and discarding the giblets, then trimming off any excess skin around the neck and body cavity. Thoroughly rinse and pat dry with paper towels. Using your fingers (or even a wooden spoon would work here), gently separate the skin from the breast meat. Place the bird breast side up in a roasting pan and set aside (and wash those hands!).
In a small bowl, stir together the butter and thyme. Quarter the lemons (start with one lemon, then use the other if necessary).
Place the lemon quarters in the body cavity of the bird. Slather some of the butter under the skin; slather the remainder of the butter on the outside of the bird, being sure not to neglect the legs, thighs and wings. Generously sprinkle the entire bird with salt and pepper.
Roast for 20 minutes per pound, or until a thermometer placed into the fattest part of the thigh reads 165 degrees. Remove from the oven, tent with foil and allow to rest for 15 minutes before slicing to allow the juices to redistribute.
Notes
Check on your birdy about halfway through cooking - if it looks like the tips of the wings and the ends of the legs are browning too much, tear off small pieces of foil and use to cover these parts of the bird. This will keep these parts from over-crisping (aka, burning) while still allowing the rest of the bird to fully cook.