Need thinned yes, where are you located? Thyme likes cool weather, but after sticking their heads above ground they will stall so the shallow root systems can grow. My thyme is already dying back since we have hit 90* here, even in shade it is hard on them. You might try using a spoon and simply scooping them into other containers, but most seeds do not like being messed with, so it is easier to just thin and reseed other spots
