If you google beurre blanc, you'll get the basic sauce recipe. At that point, you can add almost any herb or spice you care for. I'd use lemon zest rather than lemon juice at first...and then taste for flavour. You can always add more, but can never take away. As for the thyme, add it right at the end, using only fresh, please...never dried!
How can we sleep while our beds are burning???