Can I use dried thyme from a jar instead of fresh? I can't find fresh thyme anywhere.

You certainly can. I often substitute dried thyme for fresh. To get the most flavor from it, rub the dried thyme between your palms or crush it with a mortar and pestle right before adding it to the dish. This will release the herb's fragrance, making it more like fresh thyme than if used without crushing it. For this recipe, I'd leave a few uncrushed for the top, as that will make this more attractive. ;o)

Yes- thyme is one of the herbs that dries very well.