For the hens, adjust oven rack to middle position and heat oven to 400ºF (204ºC). Place a wire rack inside a large rimmed baking sheet (at least 19-by-13–inch). Reheat stuffing in a sauté pan until steaming.
Spoon ½ cup hot stuffing into cavity of each hen; tie each hens legs together with 6-inch piece of kitchen twine. Leaving as much space as possible between each hen, arrange them breast side down and wings facing out, on prepared rack-lined baking sheet. Roast until backs are golden brown, about 25 minutes.
Remove sheet from oven, spread 1 teaspoon herb butter over back of each hen. Turn hens breast side up and wings facing out, and spread 2 teaspoons herb butter over breast and leg area of each hen. Return pan to oven, add 1 cup water to sheet pan, and roast until an instant-read thermometer inserted into the stuffed cavity registers about 150ºF (65ºC), about 20–30 minutes.
Remove pan from oven again and spread 1 teaspoon herb butter over breast and leg area of each hen. Return sheet to oven, add another ½ cup water to sheet and increase oven temperature to 450ºF (232ºC).
Roast until hens are spotty brown and cavity registers 160ºF (71ºC), 15–20 minutes more, depending on hen size. (You can also check thickest parts of breast, which should register 165ºF, and thickest part of thigh, which should register 170ºF). Remove hens from oven, spread remaining butter over each hen and rest 10 minutes.