In a large skillet set over medium-high heat, melt the butter. Add celery and onions, and cook, stirring, until fragrant and softened, about 5 minutes. Stir in the parsley, sage, thyme, salt and pepper, and cook for 1 more minute. Add the chicken broth and scrape up any brown bits that have formed on the bottom of the skillet, cooking for an additional minute. Remove from the heat and cool slightly.
In a large bowl, combine the cooled mixture with the stuffing cubes and beaten eggs and mix well. Transfer the mixture to slow cooker coated with cooking spray and cover.