Hi, you can almost never use too much thyme. It is equal to one or two teaspoons. You can even sprinkle some thyme all over the turkey, it gives it a good flavor. If it is more than the recipe calls for it's alright. Trust me the turkey will be fine. I use thyme in most of my meats. It's great. Take care!
A sprig of thyme is so much less than an ounce so as not to even be considered. When you cook with thyme you typically will strip the small leaves off of the woodier stems, or boil the entire sprig and then remove the stems as you would a bay leaf.
An ounce of Thyme, is normally what would be on a stem. Thyme has a great flavour so I would not worry if you use to much, it will not ruin the recipe. Spice is joy to life, enjoy.