Ground thyme is a great substitute for dried thyme. The only difference between ground thyme and dried thyme is that ground thyme has a lot more surface area, which means its flavors disperse more readily in a dish.
Ground thyme also occupies less volume than dried thyme. Therefore, use about 90 percent of the volume in ground thyme as the recipe calls for in dried thyme. For example, if it calls for two teaspoons of dried thyme, measure out two teaspoons and remove a generous pinch. Whenever possible, however, forgo exact measurements and instead add thyme in small increments, tasting the dish until it has the desired amount of thyme flavor.