I think that the main question is, are you using the thyme as an ornamental between stepping stones or are you going to use the thyme for cooking? The Ornamec label says not to use the product on anything to be consumed as food for one year after application! The Turflon label says not to use on vegetable crops, and since it does a good job on broadleaf weeds it would probably kill your thyme. Personally, I would do my best to remove the Bermuda by hand and control the Bermuda with glyphosate when enough clear distance has been attained from the thyme; or, keep on pullin'!
hortster