cchui is right that the standard formula for substituting dried:fresh herbs is generally 1:3.
I find dried thyme, however, to be more overpowering in its dried form than most other herbs and I usually cut back even more when using it. As this is a chicken recipe rather than something with the more robust flavor of, say, beef, I'd err on the side of caution.
I wonder if anyone has an explanation why dried thyme seems to be so much stronger in that form than other herbs.
Just a guess but I'm thinking that Thyme, by percentage has more voilatile oils in a smaller area than say a leaf of Basil that is 100 or more times its size. So when Basil dries it loses a LOT of water and therefore a portion of its essence. Thyme has less water to lose when it dries so it concentrates the flavors more. The same would be true for something like Rosemary. Also the leaves of many herbs, Oregano, Parsley, Sage, Basil etc are thin, not as thick and therefore and by volume percentage again are not holding as much voilatile oils.
But then again, that's just my thought. I haven't consulted my food science book yet.